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Materiales Funcionales Nanoestructurados

Grupos de Investigación:

  • Materiales Nanoestructurados y Microestructura  (web)
  • Nanotecnología en Superficies (web)
  • Materiales para la Bioingeniería y Regeneración Tisular
  • Tribología y Protección de Superficies

Profesores de Investigación

Espinós Manzorro, Juan Pedro

jpespinos@icmse.csic.es

954 48 95 30

Grupo de Investigación:
Nanotecnología en Superficies

Fernández Camacho, Asunción

asuncion@icmse.csic.es

954 48 95 31

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Rodríguez González-Elipe, Agustín

arge@icmse.csic.es

954 48 95 28

Grupo de Investigación:
Nanotecnología en Superficies

Catedráticos

Cotrino Bautista, José

cotrino@us.es

954 48 95 77

Grupo de Investigación:
Nanotecnología en Superficies

Investigadores Científicos

Barranco Quero, Angel

angel.barranco@csic.es

954 48 95 96

Grupo de Investigación:
Nanotecnología en Superficies

Sánchez López, Juan Carlos

jcslopez@icmse.csic.es

954 48 95 79

Grupo de Investigación:
Tribología y Protección de Superficies

Yubero Valencia, Francisco

yubero@icmse.csic.es

954 48 95 97

Grupo de Investigación:
Nanotecnología en Superficies

Científicos Titulares

Borrás Martos, Ana Isabel

anaisabel.borras@icmse.csic.es

954 48 95 92

Grupo de Investigación:
Nanotecnología en Superficies

Díaz Cuenca, María Aránzazu

aranzazu@icmse.csic.es

954 48 95 42

Grupo de Investigación:
Materiales para la Bioingeniería y Regeneración Tisular

Palmero Acebedo, Alberto

alberto.palmero@icmse.csic.es

954 48 96 20

Grupo de Investigación:
Nanotecnología en Superficies

Rojas Ruiz, Cristina

tcrojas@icmse.csic.es

954 48 95 00 + ext. 90 96 25

Grupo de Investigación:
Tribología y Protección de Superficies

Investigadores/Doctores Contratados

Alvarez Molina, Rafael

rafael.alvarez@icmse.csic.es

954 48 95 76

Grupo de Investigación:
Nanotecnología en Superficies

Arzac Di Tomaso, Gisela M.

gisela@icmse.csic.es

954 48 95 00 + ext. 90 92 45

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Borrego González, Sara

sara.borrego@icmse.csic.es

954 48 95 00 + ext. 90 92 27

Grupo de Investigación:
Materiales para la Bioingeniería y Regeneración Tisular

Fortio Godinho, Vanda Cristina

godinho@icmse.csic.es

954 48 95 76

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Sánchez Valencia, Juan Ramón

jrsanchez@icmse.csic.es

954 48 95 00 + ext. 90 92 49

Grupo de Investigación:
Nanotecnología en Superficies

Becarios Predoctorales

García Valenzuela, Aurelio

aurelio.garcia@icmse.csic.es

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Paladini San Martín, Mariana

mariana.paladini@icmse.csic.es

954 48 96 31

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Personal Técnico

Rico Gavira, Victor Joaquín

victor@icmse.csic.es

954 48 96 77

Grupo de Investigación:
Nanotecnología en Superficies

Personal Contratado

De Navascués Garvin, Paula

paula.navascues@icmse.csic.es

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

García Gil, María del Rocío

mrocio.garcia@icmse.csic.es

954 48 95 31

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Gil Rostra, Jorge

jorge.gil@icmse.csic.es

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Hufschmidt, Dirk

dirk@icmse.csic.es

954 48 95 00 + ext. 90 92 45

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

López Fernández, Ester

ester.lopez@icmse.csic.es

954 48 95 00 + ext. 90 92 46

Grupo de Investigación:
Nanotecnología en Superficies

Obrero Pérez, José Manuel


954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Arquitecturas de multicapas nanostructuradas para el desarrollo de dispositivos optofluídicos sensores y procesos de funcionalización superficial avanzada (NANOFLOW)



Investigador Principal: Angel Barranco Quero y Francisco Yubero Valencia
Periodo: 31-12-2016 / 31-12-2019
Organismo Financiador: Agencia Estatal de Investigación (AEI) y Fondo Europeo de Desarrollo Regional (FEDRE)
Código: MAT2016-79866-R
Componentes: Agustín R. González-Elipe, José Cotrino Bautista, Juan Pedro Espinós Manzorro, Fabián Frutos (US), Ana I. Borrás Martos, Alberto Palmero Acebedo, Victor Rico Gavira, Ricardo Molina (IQAC-CSIC), Fernando Lahoz (ULL), Xerman de la Fuente (ICMA-CSIC), Jesús Cuevas (US), M. Fe Laguna (UPM), Antonio Rodero (UCO), M. Carmen García (UCO)

Resumen [+]

NANOFlow es un projecto multidisciplinar que persigue el desarrollo de nuevos dispositivos optofluídicos mediante la integración de materiales nanostructurados multifuncionales. El proyecto está sólidamente fundamentado en la experiencia de los componentes del grupo de investigación en campos como la síntesis de películas multifuncionales, procesos avanzados de modificación de superficies y en el desarrollo de dispositivos fotónicos multicapa. El objetivo principal de este proyecto de investigación es combinar e integrar los distintos métodos avanzados de síntesis y procesado disponibles en la fabricación de dispositivos optofluídicos singulares que sean capaces de responder a la presencia de líquidos mediante un cambio físico. La combinación de este tipo de procesos de integración junto con el desarrollo de nuevos métodos de de detección fotónica, el uso de microplasmas de gran área como fuentes de luz y de sustratos flexibles que incorporan elementos sensores definen un conjunto muy rico de posibilidades de desarrollo de aplicaciones prácticas que se explorarán en el proyecto. Además, en el proyecto también se llevarán a cabo estudios de simulación de crecimiento de películas delgadas que, en combinación con estudios de diagnosis, permitirán ajustar los procesos de crecimiento para conseguir la funcionalidades requeridas. De esta forma, el proyecto NANOFlow intenta cubrir toda la cadena tecnológica que va desde el desarrollo de nuevos materiales hasta la aplicación final incluyendo estudios de caracterización, rutas sintéticas flexibles, búsqueda de procesos alternativos de bajo costo y alto rendimiento (por ejemplo métodos de fabricación empleando plasmas a presión atmosférica), integración de dispostivos y test de éstos en condiciones reales.

Las actividades de desarrollo planteadas en NANOFlow culminan en el desarrollo de tres tipos de dispositivos innovadores como son: las etiquetas inteligentes con actividad sensora y posibilidad de usarse como sistemas de trazabilidad y anticopia (por ejemplo integrados en el empaquetado de productos alimentarios), un dispositivos optofluídico multisensor versátil y un sistema de limpieza optofluídico fotocatalítico que integra una microplasma emisor de luz, interruptores ópticos de luz UV y visible actuados por líquidos y una superficie fotocatalítica nanoestructurada. Los tres dispositivos funcionan sobre la base de una actuación o respuesta optofluídica y están diseñados para poder usarse de forma directa en sistemas de detección, manipulación y monitorización de líquidos.

Las actividades de investigación en los distintos paquetes de trabajo del proyecto y los dispositivos finales se han propuesto para responder al Reto nº 2 de la convocatoria referida a  “Seguridad y calidad alimentaria”. Además, algunas de las actividades del proyecto, por ejemplo el tercer dispositivo, están también relacionados con el Reto nº 3 “Energía Segura, eficiente y limpia”. Es interesante indicar que las actividades propuestas en NANOFlow son de particular relevancia en el contexto geográfico de Andalucía donde la agricultura, la producción de alimentos y la energía son tres de los más relevantes sectores estratégicos.


Superficies super-hielofóbicas para prevenir la formación de hielo en aeroplanos



Investigador Principal: Agustín R. González-Elipe
Periodo: 01-02-2016 / 31-01-2019
Organismo Financiador: Union Europea
Código: H2020-TRANSPORT/0149
Componentes:

Resumen [+]

La acumulación de hielo representa un grave problema para los aviones, ya que la presencia incluso de una capa apenas visible puede limitar seriamente la funcionalidad de las alas, las hélices, los parabrisas, las antenas, las rejillas de ventilación, las tomas de aire y las cubiertas. El Proyecto PHOBIC2ICE tiene como objetivo desarrollar tecnologías y herramientas de simulación predictiva para evitar o mitigar este fenómeno.
El proyecto PHOBIC2ICE, mediante la aplicación de un enfoque innovador de simulación y modelado, permitirá el diseño y fabricación de superficies hielofóbicas con funcionalidades mejoradas. Se desarrollarán varios tipos de recubrimientos poliméricos, metálicos e híbridos usando diferentes métodos de deposición. Se prepararán superficies tratadas con láser y anodizadas. En consecuencia, el proyecto se centra en la recopilación de conocimientos fundamentales sobre los fenómenos asociados con los problemas de repulsión de hielo. Este conocimiento dará una mejor comprensión del proceso de acreción de hielo en diferentes superficies modificadas y recubiertas. La infraestructura de investigación certificada (túnel de viento de hielo) y las pruebas de vuelo previstas ayudarán a desarrollar soluciones integrales para abordar la cuestión de la formación de hielo y elevarán el nivel de innovación del Proyecto.
La solución propuesta será respetuosa con el medio ambiente, contribuirá a la reducción del consumo de energía y ayudará a eliminar la necesidad de procedimientos frecuentes de deshielo sobre suelo. Esto contribuirá a la reducción del coste, la contaminación y el retraso de vuelo. 

http://cordis.europa.eu/project/rcn/199478_en.html


Un proceso completo integrado de vacío y plasma para la síntesis de celdas solares de perovskita planares y en 1D



Investigador Principal: Angel Barranco Quero
Periodo: 01-01-2016 / 31-12-2017
Organismo Financiador: Union Europea
Código: H2020-MSCA-IF-2014, Project ID: 661480
Componentes: Juan Ramón Sánchez Valencia

Resumen [+]

Las celdas solares (CS) –dispositivos que transforman luz en electricidad- han sido objeto de numerosos estudios en las últimas décadas ya que representan una prometedora vía para aprovechar la energía solar. Recientemente, las CS basadas en perovskita están recibiendo una gran atención debido a su bajo coste y alta eficiencia. Son muy prometedoras como alternativa a las actuales, pero aún necesitan avanzar para alcanzar más alta eficiencia, durabilidad y reproducibilidad, a la vez que requieren métodos de síntesis compatibles con la producción actual de dispositivos microelectrónicos a escala de oblea de silicio. Estas recientes CS son fabricadas usualmente por métodos húmedos que presentan desventajas como contaminaciones o reacciones químicas en las intercaras que pueden llevar a un deterioro del funcionamiento de la CS.

PlasmaPerovSol tiene como objetivo principal la fabricación de una celda solar de perovskita completa mediante un proceso integrado de vacío y plasma llevado a cabo bajo el concepto de un solo reactor. Los diferentes componentes de la CS se depositarán secuencialmente en un reactor de vacío evitando la exposición de los materiales e intercaras al aire o disolventes. La tecnología de deposición asistida por plasma desarrollada por el grupo receptor permite la fabricación de películas altamente conformales sobre una amplia variedad de templates.Esta aproximación se propone para fabricar multicapas conformales sobre materiales unidimensionales, con el que se mejorarán numerosos aspectos de las CS. Los procesos de vacío y plasma presentan como ventajas una alta reproducibilidad, pureza y control estequiométrico en la deposición. La síntesis propuesta es compatible con la producción a escala industrial y permite la fabricación de CS en sustratos procesables y flexibles. Al mismo tiempo, las bajas temperaturas utilizadas la hacen compatible con la tecnología actual de dispositivos microelectrónicos, y mediante el uso de máscaras permiten su integración en dispositivos preformados

http://cordis.europa.eu/project/rcn/196104_es.html

 


Desarrollo de catalizadores soportados sobre estructuras porosas para aplicaciones de generación y combustión catalítica de hidrógeno en el contexto de energías renovables



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2015-65918-R
Componentes: Asunción Fernández, Mª Carmen Jiménez de Haro, Vanda Godinho, Gisela Arzac, Dirk Hufschmidt, Rocio García

Resumen [+]

El agotamiento de combustibles fósiles a corto y medio plazo y los cambios climáticos producidos por el efecto invernadero son algunas de las principales consecuencias del uso extendido de estos combustibles. En este escenario el hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. En consecuencia se plantean actualmente retos importantes para el desarrollo de tecnologías adecuadas,  tanto en la producción de hidrógeno libre de CO2, como en su transporte y almacenamiento seguro, y en su combustión eficiente para producir calor ó electricidad en una pila de combustible. Sobre la base de los proyectos previos del grupo en el estudio de hidruros complejos para almacenamiento de hidrógeno y en el desarrollo de catalizadores y procesos integrados  de generación y uso del hidrógeno en aplicaciones portátiles; se abordarán en este proyecto nuevas investigaciones  para desarrollar catalizadores novedosos soportados sobre estructuras porosas: membranas y espumas de materiales poliméricos, metálicos y cerámicos de alto interés actual. Los catalizadores se desarrollarán y estudiarán en reacciones seleccionadas de generación y combustión de acuerdo a las siguientes líneas de actuación:

1) Desarrollo de materiales novedosos con alto valor añadido del conjunto soporte-catalizador. Por un lado los soportes porosos basados en membranas de PTFE, espumas metálicas de Ni y espumas cerámicas de SiC. El objetivo es desarrollar los nuevos catalizadores sobre soportes de interés  como membranas separadoras, electrolitos, electrodos ó combustores de hidrógeno. Los nuevos catalizadores persiguen la reducción del uso de metales nobles (i.e. bimetálicos Pt-Cu, Ni-Fe) y el desarrollo de nuevos materiales metal-metaloide (carburos, boruros, etc.). Se usarán métodos químicos de impregnación, y muy especialmente la tecnología de deposición de películas delgadas,  pulverizacón catódica, que hemos aplicado recientemente con éxito a la fabricación de catalizadores de Co. La metodología abre un campo de investigación de gran interés al permitirnos el control de la microestructura y/o la composición (i.e. Co, Co-B, Co-C) de los catalizadores a demanda.

2) La caracterización microestructural y química de los nuevos materiales y catalizadores desarrollados en el proyecto. Se trata típicamente de materiales con una microestructura y nanoestructura controlada en donde las modernas técnicas nanoscopicas van a jugar un papel fundamental en la fabricación a medida de estos.

3) Estudio de actividad en tres ensayos catalíticos: i) la generación hidrolítica de hidrógeno, ii) la descomposición fotocatalítica del agua y iii) la combustión catalítica del hidrógeno. Todas ellas reacciones de alto interés en el contexto del uso del hidrógeno como vector de transporte y almacenamiento de energías renovables.

--Sobre la base de los resultados obtenidos en estas líneas de actuación, el proyecto se ha diseñado para alcanzar un conocimiento fundamental y un diseño racional en la nanoescala de catalizadores soportados en sustratos porosos. Las relaciones composición-estructura-propiedades se investigarán usando los ensayos catalíticos y fotocatalíticos acoplados a la microscopía electrónica de alta resolución analítica y otras técnicas espectroscópicas.


Recubrimientos para aplicaciones en energía y alta temperatura



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2015-65539-P
Componentes: Iñigo Braceras Izaguirre (INASMET), Teresa Cristina Rojas Ruiz, Maria Belinda Sigüenza Carballo

Resumen [+]

La protección de las superficies frente a la temperatura, los fenómenos de oxidación o el desgaste ha logrado un progreso substancial mediante el desarrollo de nuevos materiales y recubrimientos con propiedades mejoradas tales como dureza extrema, baja fricción y tasas de desgaste, elevada resistencia ante la temperatura y la oxidación. Estas mejoras suponen un enorme ahorro de energía y reducción de costes debido a la vida media de los componentes mecánicos sin necesidad de sustitución, así como, a una reducción del impacto medioambiental. Este campo de investigación tiene una profunda repercusión en una gran variedad de sectores industriales (energía, herramientas de mecanizado, automoción, aeronáutico, metalurgia, etc.). El reto para la mayoría de estos procesos de funcionalización superficial residen en un control estricto de la micro y nanoestructura de la superficie y de las intercaras que hagan posible la aparición de nuevas propiedades y aplicaciones que la nanotecnología ofrece.

En este proyecto, se prepararán recubrimientos nanoestructurados para la protección de componentes sometidos a altas temperaturas y ambientes agresivos buscando un comportamiento mejorado. Este objetivo será abordado para tres diferentes aplicaciones que contribuirían a procesos energéticos más eficientes, energías renovables y soluciones para disminuir el impacto medioambiental. Basándonos en el sistema Cr-Al-N, se depositarán diferentes recubrimientos mediante la técnica de pulverización catódica reactiva cambiando la composición química (contenido en metal, incorporación de dopantes tales como Y o Si); microestructura; distribución de fases; arquitectura (multicapa/nanocomposite) o estructuras más complejas (tándem, multicapa en gradiente) sobre los sustratos apropiados dependiendo de la aplicación prevista: a) resistencia a la oxidación a alta temperatura (hasta 1000ºC) para herramientas; b) absorbedores solares selectivos estables térmicamente a medias (300-500ºC) y alta temperatura (>600ºC); resistencia a la corrosión para componentes en turbinas de vapor supercríticos (650ºC/100% vapor).

La investigación sobre los mecanismos de oxidación, transformaciones de fases, modificaciones estructurales, etc. serán objeto de un estudio detallado sobre los sustratos definidos para lograr un conocimiento fundamental sobre los procesos de degradación y los efectos protectores. El establecimiento de correlaciones entre las propiedades iniciales y el comportamiento funcional permitirá una mejor comprensión de los mecanismos de protección y por ende, una optimización de tales sistemas en forma de recubrimientos nanoestructurados para las aplicaciones previstas.

 

Palabras clave: Recubrimientos, alta temperatura, resistencia oxidación, corrosión, nanoestructurado, energía, absorbedor solar, multicapas


Válvulas de espín orgánicas e híbridas orgánica-inorgánicas en nanofibras soportadas, producidas por técnicas avanzadas de deposición en vacío y asistidas por plasma



Investigador Principal: Víctor López-Flores
Periodo: 01-10-2015 / 30-09-2017
Organismo Financiador: Junta de Andalucia
Código: TAPOST-234
Componentes: Supervisor: Ana Borrás Martos. Componentes: Angel Barranco Quero, Francisco Aparicio, Juan Ramón Sánchez Valencia

Resumen [+]

La transición a la electrónica orgánica requiere de nuevos elementos en la escala nanométrica compuestos por materiales orgánicos, lo que proporciona dispositivos flexibles, transparentes y baratos. Entre los dispositivos electrónicos, las válvulas de espín han destacado por su rápida transición desde la fase experimental a los productos de uso común, pero aún no se ha fabricado una válvula de espín orgánica que sea fiable. El objetivo científico de este proyecto es llenar ese vacío. Mediante el uso de métodos nanotecnológicos avanzados y escalables industrialmente, pretendemos producir una válvula de espín híbrida orgánica-inorgánica, y puramente orgánica en la forma de una nanofibra soportada de 200 nm de grosor y varias micras de longitud, con la multicapa de la válvula de espín depositada concéntricamente. Las técnicas de fabricación principales seran la deposición física en fase vapor de materiales orgánicos (O-PVD), la deposición química en fase vapor asistida por plasma (PE-CVD), y la deposición en vacío asistida por plasma remoto (RPAVD). Las medidas de magnetoresistencia se efectuarán por microscopía de fuerza atómica con sonda conductora (CP-AFM), que dará la medida definitiva de la calidad de la muestra producida.

El proyecto se desarrollará en el gripo Nanotecnología en Superficies (NanoOnSurf) del Instituto de Ciencia de Materiales de Sevilla, localizado en el centro de investigación multidisciplinar CicCartuja (Sevilla, España). Las técnicas de síntesis y cartacterización más avanzadas, desarrolladas dentro del grupo de investigación serán la clave para el éxito de este proyecto.

Este proyecto está directamente relacionado con el Programa de Trabajo Horizonte 2020, capítulo 5.i (2014-2015), acción ICT3 – 2014: “Tecnologías avanzadas en electrónica delgada, orgánica y de gran área”, y por tanto se espera un gran impacto del mismo en el futuro de la industria electrónica europea.


Aplicación de técnicas avanzadas de microscopía electrónica para la caracterización de recubrimientos nano-estructurados para aplicaciones en energías limpias



Investigador Principal: Ana María Beltrán Custodio
Periodo: 01-03-2015 / 28-02-2017
Organismo Financiador: Junta de Andalucía
Código: TAHUB-050. Programa Talent HUB
Componentes:

Resumen [+]

Este proyecto se centra en la generación y almacenamiento de hidrógeno con el objetivo de producir hidrógeno para energías limpias. Esto sucede durante una reacción exotérmica en la que es necesaria la presencia de un catalizador para que se lleve a cabo en condiciones de seguridad. Los catalizados basados en metales nobles son buenos candidatos para este objetivo (cobalto, cobre…). Aquí, los sistemas completos catalizador-soporte son estudiados. Estos sistemas son crecidos mediante técnicas de pulverización catódica (“magnetron sputtering”). La estructura y la composición son estudiadas a escala nanométrica mediante técnicas avanzadas de microscopía electrónica de transmisión-barrido (STEM), como la microscopía electrónica de alta resolución (HRTEM), imágenes adquiridas en modo campo oscuro con detector de alto ángulo (HAADF), energía dispersiva de rayos X, espectroscopia de pérdida de energía de electrones (EELS), para análisis químico. Además, el uso de la técnica de caracterización tridimensional, tomografía electrónica, aporta un completo conocimiento del sistema analizado. La combinación de técnicas de análisis estructural y de composición, en modo TEM y STEM, nos permite obtener una completa nano-caracterización del sistema. Estos análisis STEM son una herramienta esencial para determinar la relación entre la microestructura, las condiciones de crecimiento y el comportamiento final y las propiedades del sistema, que nos ayudará a mejorarlos y, por tanto, contribuir a la producción de energía limpia.

Este proyecto tiene cuatro objetivos estratégicos.

1. Nano-materiales para aplicaciones en energía limpia. Materiales para la producción, uso y almacenamiento de hidrógeno.
2. Desarrollo de la técnica de magnetron sputtering para la fabricación de nano‑estructuras (capas delgadas, recubrimientos y micro-estructuras multicapas).
3. Potenciación de las facilidades LANE (Laboratorio de microscopía del centro ICMSE-CSIC).
4. Uso de técnicas avanzadas de caracterización estructural y de análisis para el estudio a nano-escala de nuevos nano-materiales. 


Desarrollo de procesos de combustión catalítica de hidrógeno y estudio de su integración en dispositivos para aplicaciones portátiles



Investigador Principal: Asunción Fernández Camacho
Periodo: 16-05-2014 / 15-05-2016
Organismo Financiador: Junta de Andalucía
Código: P12-TEp-862
Componentes: Julián Martínez, Gisela Arzac, Dirk Hufschmidt, Joaquín Ramírez, M.Carmen Vera, Vanda Godinho, Lionel Cervera, T.Cristina Rojas, Olga Montes, Mariana Paladini, Jaime Caballero-Hernández

Resumen [+]

El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. La producción y el uso de la energía basada en la tecnología del hidrógeno es de especial relevancia en pequeña escala para aplicaciones portátiles (y potencialmente escalable para aplicaciones estacionarias). En el presente proyecto se abordará el estudio del proceso de combustión catalítica o controlada de hidrógeno en los distintos aspectos que puedan conducir a una configuración final integrada con un sistema de generación de H2 en aplicaciones portátiles. Para ello se aprovecharán las sinergias integrando investigadores de dos grupos del PAI: i) Del grupo TEP217, especialistas en almacenamiento y generación de hidrógeno en sistemas basados en hidruros metálicos, hidruros complejos y composites de hidruros reactivos; así como en el uso de catalizadores y aditivos para controlar y mejorar las cinéticas de estos procesos. ii) Del grupo FQM342, especialistas en la obtención de cerámicos porosos de alto interés como soportes de catalizadores en entornos agresivos de combustión. Además la colaboración se completa con la participación de la empresa Abengoa Hidrógeno S.A. que participa en calidad de subcontratada como especialistas en sistemas de producción y almacenamiento de hidrógeno.
En particular se trabajará en este proyecto en las siguientes líneas de actuación:
1.- Desarrollo de catalizadores y soportes para la combustión controlada. Típicamente cerámicas porosas biomórficas de carburo de silicio y catalizadores clásicos tipo metal noble y nuevos catalizadores de bajo coste a desarrollar en el proyecto.
2.- Desarrollo de los reactores necesarios para el estudio de la combustión controlada. Típicamente para flujos de hidrógeno de unos pocos ml/min y para la escala de un generador de H2 ya disponible de 0.5 a 1.5 L/min.
3.- Acoplamiento al sistema de combustión controlada de los sistemas portátiles de generación de hidrógeno que hemos desarrollado en proyectos anteriores.
4.- Aplicación de la tecnología de pulverización catódica de una manera exploratoria en este proyecto para depositar los catalizadores de combustión catalítica en sustratos porosos.
5.- Caracterización microestructural y química de los soportes y catalizadores en la nanoescala para seguir los procedimientos de síntesis y evolución en operación.
 


Plasmas de Descarga de Barrera Dieléctrica para el Desarrollo de Procesos Industriales a Presión Atmosférica (Dbd-Tech)



Investigador Principal: José Cotrino Bautista
Periodo: 30-01-2014 / 29-01-2017
Organismo Financiador: Junta de Andalucía
Código: P12-FQM-2265 (Proyecto de Excelencia)
Componentes: Francisco José García García, Jorge Gil Rostra, Richard M. Lambert, Manuel Macías Montero, Alberto Palmero Acebedo, Victor Rico Gavira

Resumen [+]

La presente propuesta de proyecto de investigación persigue en primera instancia abordar una serie de aspectos básicos no resueltos relacionados con los mecanismos de la descarga barrera, las condiciones óptimas que deben cumplir los electrodos, la definición de un diseño óptimo de los mismos y el establecimiento de las mejores condiciones para la descarga.

En una segunda instancia y desde una perspectiva aplicada, se pretende la fabricación de dos tipos de reactores de descarga barrera mejorados para dos aplicaciones tecnológicas de gran impacto industrial. Primeramente para la funcionalización superficial de materiales avanzados persiguiendo, entre otros, el control lateral de la funcionalización según patrones litográficos. En segundo término, para el desarrollo de procesos de “plasma-catálisis” tendentes a aumentar la selectividad y disminuir el consumo energético de una serie de reacciones químicas de alto valor añadido e impacto industrial. Se prevé que, para ambos tipos de aplicaciones, los estudios básicos planteados permitan avanzar de manera clara en la optimización de los procesos finales con perspectivas de uso industrial.


Control ambiental y de procesos con dispositivos responsivos con capas nanoestructuradas fabricadas por tecnologías innovadoras de vacio y plasmas



Investigador Principal: Agustín R. González-Elipe
Periodo: 01-01-2014 / 31-12-2017
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2013-40852-R
Componentes: José Cotrino Bautista, Ricardo Molina Mansilla, Victor Rico Gavira, Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Alberto Palmero Acebedo, Angel Barranco Quero, Fernando Lahoz Zamarro

Resumen [+]

Este proyecto persigue el desarrollo de una nueva generación de sistemas responsivos y sensores de baja dimensión que integren capas delgadas nanoestructuradas con propiedades ópticas y eléctricas controladas preparadas mediante técnicas innovadoras de vacío y plasma. Los principios básicos de la deposición física en fase vapor (PVD) en configuración oblicua (OAD) se extenderán a técnicas de plasma y de pulverización catódica para producir capas con porosidad controlada que interactúen  eficientemente con el medio. Se propone también la combinación de estas técnicas con otras tecnologías novedosas de plasma, como  la deposición por plasma a presión atmosférica o mediante evaporación-polimerización, para conseguir un control estricto sobre la nanoestructura y las propiedades finales de sistemaas complejos. Mediante estas tecnologías se prepararán capas finas nanoestructuradas de metales y óxidos, multicapas apiladas y nanoestructuras tipo "composites" e híbridas que, a continuación, se caracterizarán mediante microcopías electrónicas avanzadas y de proximidad, entre otras técnicas. Para encontrar nuevas rutas de procesado de capas porosas con morfologías y propiedades "a medida" y posibilitar su escalado a nivel industrial, se propone estudiar los mecanismos fundamentales que gobiernan el crecimiento de las películas a fin de modificarlos convenientemente. Conjuntos  ordenados y homogéneos de estas estructuras se emplearán como sensores de gases y líquidos a temperatura ambiente, dispositivos microfluídicos responsivos y etiquetas inteligentes. Para estas y otras aplicaciones, las capas finas porosas soportadas se funcionalizarán convenientemente con nanopartículas metálicas, cadenas moleculares ancladas o capas de  materiales poliméricos. Asímismo, se contempla su apilamiento en forma de estructuras fotónicas verticales.  Para la implementación de estas estructuras en forma de micro-dispositivos  que actúen como sensores avanzados, se desarrollarán microreactores y sistemas responsivos mediante estrategias novedosas de integración, basadas en la deposición mediante evaporación de capas eliminables de NaCl. Estos sistemas incluirán también transductores fotónicos, eléctricos y/o electroquímicos que permitan el desarrollo de dispositivos finales capaces de detectar i) oxígeno y cloro en disolución, ii) glucosa y materia orgánica en el agua, iii) vapores y gases  en aire, o iv) etiquetas inteligentes que cambien como respuesta al medio.  Se prevén aplicaciones específicas para el control del medio ambiente en aire y aguas, emplazamientos industriales e invernaderos, procesos agroindustriales  tales como la fermentación, así como para el seguimiento y la trazabilidad de diferentes tipos de mercancías y alimentos. Se espera que la combinación de nuevos descubrimientos científicos en el campo de la tecnología de capas delgadas y el de nuevos principios de integración a las escalas micro y nano abran nuevas áreas de investigación con alto impacto en diversos campos y tecnologías facilitadoras tales como la fotónica, la nanotecnología o los materiales avanzados, así como en tecnología de plasma y microfluídica.     


Nuevas nanoestructuras 1d-híbridas multifuncionales para el desarrollo de nanosistemas autoalimentados



Investigador Principal: Ana Isabel Borrás Martos
Periodo: 1-01-2014 / 31-12-2016
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2013-42900-P
Componentes: José Cotrino Bautista, Ricardo Molina Mansilla, Juan Pedro Espinós Manzorro, Ana Isabel Borrás Martos, Angel Barranco Quero

Resumen [+]

HYBR(1)D es un proyecto de carácter multidisciplinar en el que se persigue el desarrollo de nuevos materiales nanoestructurados multifuncionales que encuentren aplicación final en campos como las energías renovables, fotónica y la miniaturización de dispositivos. En el proyecto se plantea como principal objetivo el desarrollo de métodos de fabricación de nuevos materiales unidimensionales nanoestructurados como nanocables orgánicos e inorgánicos y sistemas unidimensionales heteroestructurados e híbridos. Haciendo especial hincapié en sistemas compuestos del tipo coaxial "core@shell/multi-shell" que integren componentes orgánicas, metales y óxidos. Estos materiales serán fabricados mediante una innovativa metodología que permiten su formación sobre sustratos procesables de distinta naturaleza involucrando tecnologías escalables industrialmente. Además se propone de forma exploratoria la fabricación de membranas "compuestas" que permitan el uso de estas nanoestructuras embebidas de forma autosoportada. El segundo objetivo de este proyecto es probar la funcionalidad de estas nuevas nanoestructuras en distintas aplicaciones atendiendo al concepto de “nanosistema autoalimentado”: como sistemas de generación de energía (celdas solares y piezoelectricidad) y nanosensores. Cabe resaltar que aunque los materiales a fabricar son muy diversos, desde nanotubos de semiconductores inorgánicos (TiO2 y ZnO) a nanohilos orgánicos ("small-molecule single crystal nanowires) híbridos y heteroestruturados, los métodos de fabricación que se pretenden utilizar se basan en técnicas de vacío muy similares y facilmente acoplables. Así, las distintas nanoestructuras y heteroestructuras se fabricarán mediante cuatro técnicas principales y combinaciones de las mismas: deposición física desde fase vapor aplicada a moléculas orgánicas, deposición química desde fase vapor asistida por plasma de moléculas orgánicas y óxidos semiconductores, sputtering-dc de metales y "etching" por plasma de oxígeno. El IP y el grupo Nanotechnology on Surfaces del ICMS tienen un amplio background en la aplicación de estas técnicas para el desarrollo de sistemas del tipo láminas delgadas y recubrimientos funcionales, experiencia que se ha extendido en los últimos años al estudio de nanoestructuras 1D soportadas. El proyecto aborda toda la cadena de valor que lleva desde la síntesis de nuevos materiales a sus aplicaciones, incluyendo su caracterización avanzada e integración en dispositivos y prototipos a escala de laboratorio.


Nuevos materiales para envasado, etiquetado inteligente, control de fraudes y monitorización visual del estado de los productos



Investigador Principal: Angel Barranco Quero
Periodo: 02-12-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: RECUPERA2020 - 1.4.2
Componentes: Ana Isabel Borrás, Francisco Yubero, José Co-trino, Juan Pedro Espinós, Juan Ramón Sánchez Valencia, Francisco Javier Aparicio Rebollo

Resumen [+]

En esta actividad se pretende desarrollar una serie de nuevos materiales y procesos basados en marcado por láser para el desarrollo de un nuevo sistema de marcaje y etiquetado “inteligente” capaz de lograr una mejora en los procesos de control y de la trazabilidad de productos agropecuarios.


Purificación del aire en invernaderos y centros de tratamiento de alimentos



Investigador Principal: José Cotrino Bautista
Periodo: 2-12-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: RECUPERA2020 - 2.2.3
Componentes: Ana María Gómez Ramírez, Antonio Méndez Montoro de Damas

Resumen [+]

Este proyecto está relacionada con una tecnología para generar un plasma frío a presión atmosférica con aire que fluye a través de un reactor. El objetivo específico de esta actividad es el desarrollo de un sistema prototipo de purificación de aire para invernaderos, centros de procesamiento de alimentos, recintos para el ganado u otros tipos similares en mercados o recintos donde la concentración de gases nocivos para la salud de los trabajadores puede ser muy significativa por el uso de insecticidas, fungicidas, desinfectantes y otros compuestos. El sistema desarrollado debe ser capaz de purificar el aire en instalaciones cerradas y donde un gran número de productos químicos, compuestos orgánicos volátiles, principalmente, se acumulan en el aire del establecimiento. El diseño de la tecnología del reactor de plasma frío sigue las características de descarga de barrera dieléctrica con dieléctrico en forma de lecho empaquetado utilizando materiales dieléctricos de carácter ferroeléctrico con elevada constante dieléctrica.


Sensores micro-fluídicos integrados para el control de la fermentación



Investigador Principal: Agustín R. González-Elipe
Periodo: 2-12-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: RECUPERA2020 - 1.4.1
Componentes: Juan Pedro Espinós Manzorro, José Cotrnio Bautista, Francisco Yubero Valencia, Alberto Palmero Acebedo, Angel Barranco Quero, Ana I. Borrás Martos, Victor J. Rico Gavira, Rafael Alvarez Molina, Pedro Angel Salazar Carballo

Resumen [+]

El objetivo de este proyecto es el desarrollo de nuevos sistemas micro/nano fluídicos integrados y robustos que permitan la incorporación fiable de tests de control, sensorización y/o análisis rápido de productos agroalimentarios, fundamentalmente líquido o productos solubles. La tecnología a desarrollar se intenta aplicar tanto para el control de productos finales como durante las etapas de elaboración de los mismos. En concreto, un nicho de aplicación que directamente que se abordará dentro del proyecto es el control de procesos de fermentación, con el desarrollo de nuevos transductores fluídicos integrados que permitan la detección cuantitativa de glucosa y/o otros azúcares mediante desarrollos electroquímicos y fotónicos en dispositivos microfluídicos y similares.


Nuevos materiales para envasado, etiquetado inteligente, control de fraudes y monitorización visual del estado de los productos



Investigador Principal: Angel Barranco Quero
Periodo: 01-12-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: RECUPERA2020 - 1.4.2
Componentes: Ana Isabel Borrás, Francisco Yubero, José Cotrino, Juan Pedro Espinós, Juan Ramón Sánchez Valencia, Francisco Javier Aparicio Rebollo

Resumen [+]

En esta actividad se pretende desarrollar una serie de nuevos materiales y procesos basados en marcado por láser para el desarrollo de un nuevo sistema de marcaje y etiquetado “inteligente” capaz de lograr una mejora en los procesos de control y de la trazabilidad de productos agropecuarios.


Dispositivos luminiscentes basados en láminas delgadas con tierras raras depositadas mediante tecnología de plasma (LUMEN)



Investigador Principal: Angel Barranco Quero
Periodo: 16-05-2013 / 15-05-2016
Organismo Financiador: Junta de Andalucía
Código: P11-TEP-8067 (Proyecto de Excelencia Motriz)
Componentes: Agustín R. González-Elipe, Juan Pedro Espinós, Richard Lambert, Juan Carlos González-González, Francisco J. García García, Victor J. Rico Gavira, , Jorge Gil Rostra, Lola González García, F. Javier Ferrer (CNA), Fabián Frutos Rayego

Resumen [+]

El presente proyecto persigue el desarrollo de una serie de dispositivos luminiscentes basados en láminas delgadas con tierras raras depositadas mediante tecnologías de plasma. Las láminas delgadas luminiscentes se fabricarán mediante un nuevo procedimiento desarrollado por el grupo investigador que combina procesos clásicos como “magnetrón sputtering” o deposición por plasma y la evaporación de compuestos metalorgánicos de baja o nula tensión de vapor a temperatura ambiente pero fácilmente sublimables en la cámara de reacción. Esta metodología ofrece la oportunidad de integrar uno o varios elementos de tierras raras dentro de la capa formada, controlando perfectamente su concentración en la misma. Dada la versatilidad del proceso, se plantea fabricar capas delgadas luminiscentes de interés para tres campos de aplicación: procesos de “up conversión”, detectores de ion-luminiscencia y sistemas de señalización. Los materiales a desarrollar deben permitir superar algunas de las limitaciones existentes con los materiales actualmente existentes, proporcionando nuevas funcionalidades y mejoras sustanciales en sus prestaciones en relación con aplicaciones como detectores en procesos de fusión nuclear, cambiadores de longitud de onda en sistemas para comunicaciones ópticas y señalización en automoción.  Dadas las características del nuevo método propuesto, el proceso de síntesis de las capas luminiscente es compatible con otros procesos en línea proponiéndose la integración de las capas luminiscentes en dispositivos fotónicos simples formadas por estructuras multicapa tipo reflectores de Bragg o similares.  El proyecto aborda todo la cadena de valor que lleva de la síntesis de los materiales a sus aplicaciones, incluyendo su caracterización avanzada, el análisis de sus propiedades ópticas y de luminiscencia, su integración en dispositivos y el análisis de su resistencia medioambiental.


Desarrollo de nuevos materiales y procesos para la generación y uso del hidrógeno principalmente en aplicaciones portátiles



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-01-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2012-32519
Componentes: Gisela Arzac, Jaime Caballero, Lionel Cervera, Vanda Fortio, Carlos Negrete, Dirk Hufschmidt, Cristina Rojas Ruiz, Roland Schierholz

Resumen [+]

El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. En el presente proyecto se abordará el estudio de los distintos procesos que conducen a la configuración final integrada de sistemas de generación y uso del hidrógeno principalmente en aplicaciones portátiles (y potencialmente escalables para aplicaciones estacionarias). En particular se trabajará en este proyecto en las siguientes líneas de actuación:
a) Investigación en nuevos compuestos ligeros para su uso en procesos de generación de hidrógeno en pequeña escala por vía química (hidrólisis). Típicamente reacciones de hidrólisis de borohidruros (i.e. NaBH4) y compuestos tipo borano de amoníaco, hidrazinas ó borano hidrazina. Este area incluye el desarrollo de catalizadores en la nanoescala utilizando métodos de vía húmeda para su síntesis: Nanoestructuras metal-metaloide (tipo Co-B, Co-B-P y similares) y catalizadores bimetálicos (que incluyan ó no metaloide) de bajo coste potenciando efectos sinérgicos (tipo CoRu, NiPt ó Co-Ru-B). Incluye también el desarrollo de reactores portátiles para estos procesos y el desarrollo de nuevos sustratos y monolitos, estudios de adherencia del catalizador y durabilidad.
b) Investigación en nuevos sistemas anfitrión-huésped (host-guest) que contengan hidrógeno para el almacenamiento reversible (carga/descarga). Principalmente soportes (anfitrión) porosos del tipo “nanoscaffolds” (basados en C ó BN) infiltrados con borohidruros (huésped) (i.e. borohidruro de titanio) típicamente utilizados para el almacenamiento reversible de hidrógeno. Estos nuevos materiales deben presentar cinéticas de carga y descarga mejoradas.
c) Estudios de acoplamiento de un sistema generador de hidrógeno de bajo coste a una celda de combustible. Típicamente un reactor continúo para la hidrólisis del NaBH4 con catalizador Co-B que suministra H2 en condiciones de flujo constante para alimentar directamente una pila de combustible tipo PEM de 60 W.
d) Estudios fundamentales para el desarrollo de catalizadores y soportes para la combustión controlada de hidrógeno. Es una línea nueva en el grupo de investigación que se basa en preparar por vía húmeda catalizadores nanoparticulados de metal noble sobre soportes comerciales de cerámicas porosas (tipo SiC). Incluye el diseño de un reactor para el estudio en escala laboratorio de la producción de calor por combustión controlada de hidrógeno.
e) Desarrollo de la tecnología de pulverización catódica (“magnetrón sputtering”) para la preparación de catalizadores y nano-estructuras sobre diversos sustratos de aplicación en los procesos desarrollados en los apartados anteriores. El grupo tiene una amplia experiencia en esta tecnología que se aplicaría de manera novedosa en este proyecto permitiendo una gran versatilidad en cuanto a la nanoestructura, composición y aditivos para mejorar la actividad, durabilidad y selectividad de los catalizadores.
f) Caracterización microestructural y química de los nuevos materiales y catalizadores desarrollados en el proyecto. Se trata típicamente de materiales con una nanoestructura controlada en donde las modernas técnicas nanoscopicas van a jugar un papel fundamental en la fabricación a medida de estos materiales.
 


Arquitecturas SOFC innovadoras basadas en operación "Triodo"



Investigador Principal: Agustín R. González-Elipe
Periodo: 01-09-2012 / 29-02-2016
Organismo Financiador: Unión Europea
Código: FCH-JU-2011-1
Componentes: Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Angel Barranco Quero, Richard Lambert, Victor J. Rico, Ana Borrás Martos, José Cotrino, Jorge Gil, Pedro Castillero, Fran J. García, Alberto Palmero

Resumen [+]

El desarrollo de celdas de combustible de óxido sólido (SOFCs) que operen con hidrocarburos como combustibles (gas natural, biocompustibles, LPG) es esencial para la comercialización a plazos cortos y medios. El desarrollo de HC SOFCs directas se enfrenta todavía a numerosos retos y problemas que surgen del hecho que los materiales del anodo operan bajo condiciones muy severas. Estas limitan el rendimiento con reacciones de reformado u oxidación, producen una desactivación rápida debido a la contaminación con carbón y generan inestabilidad asociada a la presencia de compuestos de azufre. Aunque la investigación en estos temas es intensa, no se han producido avances tecnológicos significativos respecto a mejorar la robustez del proceso, el incremento de su tiempo de vida y a la disminución de su costo.

T-CELL propone una aproximación electroquímica novedosa con el fin de abordar estos problemas mediante un esfuerzo integrado para definir, explorar, caracterizar, desarrollar y ejecutar una aproximación a la tecnología SOFC radicalmente nueva basada en una aproximación tipo “triodo”. Para ello se desarrollará una aproximación integrada basada en el desarrollo de materiales y en la aplicación de un diseño de celda innovador que permite el control efectivo de la actividad electrocatalítica bajo vapor o condiciones de reformado en seco.
La novedad del trabajo propuesto reside en el esfuerzo pionero para desarrollar nuevos materiales a base de Ni que actúen como ánodo y que presenten tolerancia al envenenamiento, así como en el desarrollo del concepto de triodo aplicado a celdas SOFC para incorporar una nueva variable en la operación de celdas de combustible.
Para demostrar la posibilidad de apilamiento en las celdas triodo, se desarrollará un apilamiento SOFC tipo triodo formado por cuatro unidades repetidas. Este sistema se evaluará con metano y vapor en presencia de una pequeña concentración de compuestos de azufre.
 


Desarrollo de recubrimientos nanoestructurados protectores para su uso en condiciones extremas (NANOPROTEXT)



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-01-2012 / 31-12-2014
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2011-29074-C02-01
Componentes: T. Cristina Rojas Ruiz; Francisco Javier Pérez Trujillo;Maria del Pilar Hierro de Bengoa;Germán Alcalá Penades; Maria Sonia Mato Díaz; Marta Brizuela; Pablo Corengia; José Luis Viviente; Alberto García;Daniel González

Resumen [+]

En muchas operaciones industriales, los componentes de las maquinas o piezas que están en contacto se hallan sometidos a condiciones extremas de carga, fricción, temperatura o atmósfera variable. La investigación dirige sus esfuerzos hacia al desarrollo de nuevos recubrimientos multicomponentes capaces de aumentar su eficiencia protegiendo su superficie contra el desgaste y la oxidación, que ocasionan fallos ulteriores de funcionamiento. Mediante el control del tamaño y distribución de las fases componentes, la composición química y su microestructura en el rango nanométrico es posible obtener propiedades multifuncionales tales como baja fricción, dureza y estabilidad térmica.
En este proyecto se propone el desarrollo de tres tipos de recubrimientos nanoestructurados mediante el proceso de magnetron sputtering para aplicaciones protectoras en condiciones extremas o singulares de funcionamiento (presión, temperatura, atmósferas oxidantes, vacío, etc). Los sistemas elegidos comprenden cristales de materiales duros (nitruros o carburos) combinados con una segunda fase o elemento que mejore su comportamiento. De este modo se ensayarán recubrimientos nanocomposite formados por nanocristales de WC dispersos en una segunda fase amorfa de tipo calcogenuro (WS2 or WSe2) para su uso como lubricante sólido en aplicaciones espaciales o bajo atmósferas inertes. En el segundo caso, Y ó Zr serán usados como elementos dopantes dentro de recubrimientos de CrAlN con objeto de incrementar la resistencia a la oxidación a baja y alta temperatura, y el comportamiento tribológico, muy válido en numerosos sectores industriales tales como (herramientas de mecanizado, metalúrgico, aeronaútico, automoción, etc.). Finalmente, se desarrollaran recubrimientos nanocomposite duros y transparentes basados en la familia del Al-Si-N para protección de sistemas ópticos.
En todos los casos, el proyecto comprende su síntesis, caracterización estructural y química, así como su validación práctica en ensayos tribológicos y de oxidación que simulan las condiciones finales de operación. En el caso concreto de las capas duras y transparentes también se evaluarán sus propiedades ópticas. El estudio de la relación existente entre la microestructura y las propiedades medidas será un objetivo esencial puesto que permitirá una mayor comprensión de los mecanismos de actuación, y por ende, la optimización de tales sistemas nanoestructurados para su mejor aprovechamiento tecnológico.
 


Laboratorio avanzado para el análisis de nanomateriales funcionales



Investigador Principal: María Asunción Fernández Camacho
Periodo: 01-10-2011 / 30-03-2015
Organismo Financiador: Unión Europea
Código: REGPOT-CT-2011-285895
Componentes: T. Cristina Rojas, M.Carmen Jiménez, Gisela Arzac, Olga Montes, Inmaculada Rosa, Rafael Alvarez, Vanda Godinho, Juan Carlos Sánchez-López, Hernán Míguez, Agustín R. González-Elipe, Manuel Ocaña, M. Jesús Sayagués, Lionel Cervera, Roland Schierholz, Salah Rouillon, Lucia Castillo, Rocío García, Carlos García-Negrete, Jaime Caballero

Resumen [+]

El proyecto AL-NANOFUNC ha sido diseñado para poner en marcha en el Instituto de Ciencia de los Materiales de Sevilla (ICMS, CSIC-Univ.Sevilla, España) un laboratorio avanzado para el Nano-análisis de nuevos materiales funcionales. Las técnicas de Nanoscopía avanzada, basadas en equipos de microscopía electrónica de última generación, se dedicarán a la investigación de vanguardia en temas específicos de gran interés: i) Nanomateriales para aplicaciones energéticas sostenibles; ii) películas delgadas multifuncionales y recubrimientos nanoestructurados; iii) materiales nano-estructurados para fotónica y sensores. Para situar a los laboratorios del ICMS en una posición de liderazgo que sea competiti-va en un escenario mundial, el proyecto AL-NANOFUNC contempla la puesta al día del poten-cial investigador actual en varias direcciones: i) Mejorar las capacidades de equipamiento en relación a la microscopía electrónica analítica de alta resolución; ii) mejorar el impacto de la investigación básica a través de la contratación de investigadores especializados y el intercambio transnacional con los centros de referencia en Europa, iii) desarrollar y mejorar el potencial de innovación de la investigación del ICMS abriendo las nuevas instalaciones a empresas y centros relacionados; iv ) organizar talleres, conferencias y actividades de difusión para mejorar la visibilidad de la investigación. En el proyecto se propone también una estrecha colaboración con centros de referencia y empresas de Lieja (Bélgica), Graz (Austria), Jülich (Alemania), Oxford (Inglaterra), Cambridge (Inglaterra), Dübendorf (Suiza) y Rabat (Marruecos), así como con laboratorios de Universidades Andaluzas. Cinco empresas en Andalucía colaborarán también en estrecha sinergia para promover las líneas estratégicas de interés a largo plazo de la región en los productos de piedra natural y artificial y los sectores de energía solar y energías renovables.


Recubrimientos nanoestructurados para operar en vacío



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-10-2011 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2010-21597-C02-01
Componentes: T. Cristina Rojas Ruiz, Santiago Domínguez Meister

Resumen [+]

En este proyecto se desarrollarán recubrimientos nanoestructurados por la técnica de magnetron sputtering para lubricación de componentes mecánicos en aplicaciones aeroespa-ciales. Estos materiales deben proporcionar protección frente al desgaste y baja fricción cuando se usen en condiciones atmosféricas o vacío. Los sistemas elegidos para lograr este compromiso están formados por nanocristales de WC dispersados en una fase amorfa de dicalcogenuro (WS2 or WSe2). Estos lubricantes se esperan que pueden mejorar la resistencia al desgaste, mecánica y a la oxidación en comparación con los recubrimientos convencionales (MoS2 or DLC) usados para estos fines.


Desarrollo de recubrimientos y andamios bioactivos de material cerámico nanoestructurado para la regeneración ósea (BIOCEREG)



Investigador Principal: María Aránzazu Díaz Cuenca
Periodo: 06-07-2011 / 05-06-2016
Organismo Financiador: Junta de Andalucía
Código: CTS-661
Componentes: M. Lourdes Ramiro Gutiérrez, Sara Borrego González

Resumen [+]

Este Proyecto pretende contribuir al avance en el desarrollo de nuevos biomateriales con bioactividad mejorada para su aplicación en la reparación y regeneración ósea. Se propone la preparación de nuevos recubrimientos y andamios cerámicos mediante técnicas de procesado láser a partir de materiales cerámicos particulados, nanoestructurados de composición bioactiva en el sistema SiO2-CaO-P2O5 sintetizados en el ICMS por la Dra. Díaz (IP de esta solicitud). La hipótesis de partida es que las características nanoestructurales y texturales del material cerámico particulado en combinación con la fuente láser tiene un gran potencial para resultar en deposiciones con microestructura y nanoestructura controlada. Se plantea procesar dos tipos de pieza prototipo: i) piezas de sustrato metálico (de titanio) con recubrimiento cerámico de composición bioactiva y ii) piezas monolito (andamio) solo cerámica bioactiva con geometría controlada. Hay que distinguir por tanto la persecución de dos hitos. Un primer Hito es la obtención de materiales prototipo (recubrimientos y andamios) con unos requerimientos de micro y nanoestructura, superficie, propiedades mecánicas, homogeneidad y reproducibilidad mínimas. Y un segundo Hito consistente en la verificación de sus propiedades biológicas in vitro e in vivo. El éxito en ambos hitos es lo que finalmente denominaremos biomaterial prototipo. La obtención de los recubrimientos tendría una translación muy directa para implementarse en distintas partes de los componentes de implantes ortopédicos. En este sentido el equipo de investigación integra a biólogos de regeneración esquelética y clínicos de cirugía ortopédica y traumatología que van a estudiar la bioactividad y biocompatibilidad de estos recubrimientos sobre sustratos de titanio suministrados por Synthes, empresa líder en fabricación y comercialización de implantes para ortopedia, que participa en esta propuesta como EPO. Por otra parte y desde el punto de vista del procesado de materiales, la aplicación del procesado láser a los materiales cerámicos nanoestructurados SiO2-CaO-P2O5 es totalmente novedoso y creemos que puede optimizarse para obtener recubrimientos y también andamios tridimensionales, conformados con macroporosidad interconectada pero a su vez con microestructura fina y nanoestructura, que culminen en la obtención de piezas prototipo con alta reproducibilidad y de calidad e innovación tecnológica elevada. El Proyecto se encuadra en áreas de investigación fuertemente innovadoras y pujantes como son la nanotecnología y la medicina regenerativa ambas con un carácter multidisciplinar intrínseco donde la frontera entre las distintas disciplinas científicas tradicionales aparece difuminada. El Proyecto aúna esfuerzos de investigadores con formación básica en las disciplinas de química (ICMS), física e ingeniería (Empresa Subcontratada AIMEN), biología (UMA-CIBER-BBN) y medicina clínica y traslacional (HCS). Creemos que la integración de estos tres pilares i) síntesis, procesado y caracterización de materiales, ii) biología de la regeneración e ingeniería tisular y iii) práctica clínica ofrece una propuesta con capacidad para aportar resultados de impacto trasferibles a la industria y que puede por tanto ayudar al desarrollo de productos para aplicaciones en la reparación y rege-neración esquelética en Andalucía.


Sol y Visión par la energía térmica actual. SOLVENTA



Investigador Principal: Agustín R. González-Elipe
Periodo: 4-05-2011 / 31-12-2014
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: Proyecto INNPACTO - IPT-2011-1425-920000
Componentes: Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Angel Barranco Quero, Victor J. Rico, Ana Borrás Martos, José Cotrino, Jorge Gil, Pedro Castillero, Fran J. García

Resumen [+]

Este proyecto persigue el desarrollo de una serie de equipos y dispositivos para la monitorización de las condiciones de funcionamiento de plantas termosolares de concentración con espejos cilíndrico-parabólicos. La participación del ICMSE se centra en la aplicación tecnologías de plasma y el desarrollo de sistemas en lámina delgada capaces de diagnosticar las condiciones de funcionamiento de dichas instalaciones.


Control de procesos en plasmas para la síntesis de materiales nanoestructurados en forma de láminas delgadas (PLASMATER)



Investigador Principal: Alberto Palmero Acebedo
Periodo: 15-03-2011 / 14-03-2014
Organismo Financiador: Junta de Andalucía
Código: P09-FQM-6900
Componentes: José Cotrino Bautista, Ana Borrás Martos, Francisco Yubero Valencia, Rafael Alvarez Molina, Juan Carlos González González, Carmen López Santos

Resumen [+]

En el proyecto PLASMATER abordamos el desarrollo de nuevos procesos basados en plasmas para controlar la nanoestructura, porosidad y morfología superficial de películas del-gadas, con el objetivo de mejorar sus funcionalidades para aplicaciones finales. En las técnicas de deposición de películas delgadas asistida por plasma, las cantidades que definen la deposi-ción, tales como la potencia electromagnética empleada, presión de los gases, etc., definen las propiedades del plasma, que a su vez, y a través de procesos no-lineales y fuertemente acoplados entre sí, produce el crecimiento de la película delgada en un porta-substrato. La complejidad de todos estos procesos ha dado lugar a que existan multitud de relaciones de carácter empírico entre cantidades controlables experimentales y las nanoestructuras crecidas, sin que haya una explicación clara sobre los mecanismos que controlan dicho crecimiento, y la conexión entre ambas. Este conocimiento es esencial para proponer modificaciones en las condiciones de la deposición que permitiesen un mayor control y versatilidad a la hora de sintetizar películas delgadas nanoestructuradas. En PLASMATER nos proponemos desarrollar herramientas para controlar procesos en plasmas y obtener capas nanoestructuradas y sistemas 1D de TiO2 y ZnO soportados en subs-tratos, para mejorar propiedades funcionales tales como foto-actividad o propiedades de mojado, entre otras. Se explorarán tres aspectos relacionados entre sí: i) diagnosis completa de la fase gaseosa (plasma y vaina) y caracterización de la nanoestructura de los materiales depositados, ii) estudio de las funcionalidades de dichos materiales, y iii) el desarrollo de códigos numéricos predictivos, a partir de los cuales se desarrollen nuevos protocolos que permitan un mayor control sobre la nanoestructura del material y, por lo tanto, sobre las funcionalidades. El uso de modelos predictivos tiene una gran relevancia debido a que, hasta nuestro conocimiento, i) será la primera vez en la literatura que se dé una visión completa del proceso de deposición y nanoestructuración de estas películas delgadas basada en fenómenos fundamentales, a partir del valor de las cantidades experimentales de control (potencia electromagnética empleada, presión de los gases, etc.), y ii) se utilizará el modelo para proponer modificaciones en el proceso de deposición que ayuden a controlar los procesos de nanoestructuración de la película y proveer de más flexibilidad y versatilidad a los materiales depositados con vista a mejorar sus funcionalidades. Para desarrollar el proyecto PLASMATER nos proponemos seguir una estrategia mixta simulación/diagnosis experimental del proceso de deposición para desarrollar interactivamente los modelos de crecimiento en múltiples condiciones. Se considerará el estudio de las diferentes escalas espaciales en el problema, desde el propio plasma (escala típica de decenas de centímetros), la vaina del plasma (por debajo de 1 milímetro), y la superficie del material (decenas de nanometros), y se utilizarán herramientas de diagnostico avanzado del plasma y de la película delgada que ayudarán al desarrollo del proyecto. Por último, la investigación también se centrará en encontrar las condiciones experimentales que permitan obtener la mejores propiedades de las capas con vista a optimizar sus aplicaciones tecnológicas e industriales.


Desarrollo de recubrimientos composite de carbono para aplicaciones biomédicas



Investigador Principal: Juan Carlos Sánchez López
Periodo: 15-03-2011 / 15-03-2014
Organismo Financiador: Junta de Andalucía
Código: P10-TEP 06782
Componentes: T. Cristina Rojas, Carlos López Cartes, David Abad, Vanda Godinho, Santiago Domínguez, Inmaculada Rosa

Resumen [+]

El proyecto comprende el desarrollo de recubrimientos basados en carbono desde su síntesis a medida, caracterización, evaluación en tests de desgaste y estudios de biocompatibilidad para su uso en implantes artificiales. El control del tipo de enlace químico del carbono (sp2/sp3) y la composición química, incluyendo metales como (Ag, Ti) u otros elementos (B, N, O), permitirá modular las propiedades mecánicas y tribológicas (dureza, fricción y resistencia al desgaste) con objeto de incrementar su comportamiento final. Para ello se propone el empleo de la técnica de pulverización catódica (del inglés magnetron sputtering) para depositar estos recubrimientos avanzados sobre los materiales usados en los implantes (acero, aleaciones de Ti o polímeros) bajo diferentes condiciones de síntesis. Seguidamente, éstos composites de carbono serán evaluados de forma comparativa en ensayos de fricción y desgaste que simulen las condiciones que estos materiales se encontrarán en la aplicación final. De esta manera será posible establecer una correlación entre el comportamiento observado y las características químicas y estructurales de las capas preparadas bajo diferentes condiciones de síntesis. Finalmente, la biocompatibilidad será estudiada en ensayos de adhesión celular, citotoxicidad y actividad antibacteriana. Este completo conjunto de análisis aportará una excelente perspectiva de las posibilidades de transferencia tecnológica de estos materiales avanzados a la biomedicina.


Láminas delgadas porosas funcionales y nanoestructuras 1D soportadas de óxidos para el desarrollo de microfluídica en lámina delgada, válvulas fotónicas y micro plasmas (POROUSFILMS)



Investigador Principal: Francisco Yubero Valencia
Periodo: 01-01-2011 / 31-12-2013
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2010-18447
Componentes: Agustín R. González-Elipe, Juan Pedro Espinós Manzorro, Alberto Palmero Acebedo, Rafael Alvarez Molina, Juan Carlos González González, Victor J. Rico Gavira, Jorge Gil Rostra, Ana Isabel Borrás Martos, Lola González García, José Cotrino Bautista

Resumen [+]

En este proyecto se prepararán láminas delgadas de TiO2, ZnO, SiO2 y SnO2 dopado, así como nanostructruras de fibras soportadas de estos óxidos mediante deposition por plasma y por evaporación a ángulo rasante (GLAD). Se controlará la nano- y micro-estructura de las capas y fibras mediante la selección de las condiciones adecuadas de deposición usando GLAD y, en el caso de la deposición mediante plasma, tras ajustar y modelizar el plasma y sus principales parámetros de operación, así como los fenómenos ligados a la vaina del plasma y su influencia en el desarrollo de la nanoestructura de las capas y fibras. El primer objetivo del proyecto es conseguir controlar la porosidad y otras propiedades críticas (ópticas, conductividad eléctrica, comportameinto frente al mojado, etc.) de los materiales sintetizados para propiciar el desarrollo de nuevos métodos de manejo de fluidos (líquidos y gases) a escalas micro y, posiblemente, nanométricas de manera de inventar y desarrollar aplicaciones en los campos de microfuídica y microplasmas. Un objetivo adicional es el procesado de estas estructuras tanto en una aproximación 2D (procesado litográfico) como 3D mediante el uso de técnicas basadas en láser, el apilamiento en multicpas de diferentes estrucuras de capas finas porosas y/o la deposición selectiva de zonas hidrofóbicas de otros materiales tales como polímeros, siliconas, etc. A partir de estas estructuras se desarrollarán dispositivos microfluídicos basados en láminas delgadas porosas de TiO2 y ZnO activadas con luz (válvulas fotónicas). Estos materiales se vuelven superhidrofílicos cuando se iluminan con luz de <390 nm que, usada para iluminar ciertas áreas pequeñas del material (canales, circuitos micrométricos, etc.) usando lámparas adecuadas o un láser, permitirá activar selectivamente esas zonas. El desarrollo de microfiltración controlada por luz es otra nueva aplicación en este campo que debe permitir la difusión/filtración preferente de líquidos polares a través de las zonas iluminadas (válvula abierta). Conseguir una rápida reversión de este proceso (válvula cerrada) is otro reto que se abordará dentro del proyecto. Un objetivo final de carácter exploratorio es el modelado, diseño y desarrollo de mi-croplasmas basados en las estrucutras porosas en forma de capa delgada desarrolladas durante las etapas iniciales del trabajo. Estos prototipos de microplasmas estarán formados por electrodos de capas porosas de SnO2 dopadas permeables a gases y capas aislantes porosas de SiO2 que actuarán como barreras de separación. La evaluación de las caracterísitcas del plasma en estos dispositivos prototipo será una acción addicional que se abordará en el proyecto.


Nuevas técnicas de procesado en cerámica y vidrio respetuosas con el medio ambiente (CERAMGLASS)



Investigador Principal: Xermán F. de la Fuente Leis
Periodo: 1-01-2011 / 31-12-2014
Organismo Financiador: Ministerio de Economía y Competitividad
Código: LIFE11 ENV/ES/560
Componentes: ICMS: Agustín R. González-Elipe, Victor J. Rico, Angel Barranco Quero, Juan Pedro Espinós Manzorro, Jorge Gil, Francisco Yubero Valencia

Resumen [+]

El objetivo general del proyecto CERAMGLASS es disminuir el impacto al medio ambiente durante los tratamientos térmicos en la industria cerámica mediante la aplicación de una tecnología innovadora de horno láser a cerámica plana y vridrio. El proyecto persigue construir una planta piloto basada en la combinación innovadora de un horno continuo y un láser que barra la superficie. El propósito es probar que esta combinación permite una reducción significativa en el consumo energético y la escalabilidad industrial del proceso.
En primer lugar, el proyecto persigue demostrar que es posible producir placas cerámicas robustas de sólo 4 mm de espesor. Esto significaría una reducción del 50% en el espesor, con la consiguiente reducción en el consumo de materias primas. El proyecto persigue también adaptar las composiciones decorativas incorporando el uso de materiales menos agresivos al uso del procesado láser. En concreto, se tratará de adaptar los procesos de decorado “screen printing” a productos de tercer fuego con lustre y efectos metálicos, así como el de tintas decorativas al vidrio plano. La sustitución de productos iniciales tóxicos permitirá una disminución en la generación de CO2 y otras emisiones gaseosas, residuos tóxicos y la reducción de los requerimientos energéticos del proceso.
 


Síntesis mediante plasma CVD de nuevos materiales orgánicos nanoestructurados integrado en dispositivos planares para aplicaciones como sensores fotónicos y de marcaje de seguridad NANOPLASMA



Investigador Principal: Angel Barranco Quero
Periodo: 01-01-2011 / 31-12-2013
Organismo Financiador: Ministerio de Ciencia e Innovación. Programa  FEDER Unión Europea
Código: MAT2010-21228
Componentes: Ana Borrás Martos, Agustín R. González-Elipe, Carmen Ruiz, M. Carmen López-Santos

Resumen [+]

En NANOPLASMA se propone el desarrollo de nuevas técnicas basadas en plasmas para la síntesis y procesado de nuevos materiales funcionales orgánicos. La tecnología de plasma para síntesis de materiales actualmente en uso, como el CVD activado por plasma (PECVD) o los procesos de polimerización por plasma, implica siempre la fragmentación completa de un precursor volátil. En contraste NANOPLASMA persigue la síntesis de una nueva familia de materiales luminiscentes en forma de película delgada o nanocables 1D soportados, mediante el control químico y del proceso de fragmentación en la zona remota de una descarga de plasma. La investigación se centrará en la síntesis de matrices orgánicas con microestructura nanométrica controlada que incorporan moléculas orgánicas luminiscentes (por ejemplo perilenos, rodaminas, ftalocianinas y porfirinas) y nanocables orgánicos 1D a partir del mismo tipo de moléculas. El proyecto también contempla el desarrollo de metodologías basadas en procesos de etching por plasma y ablación láser, para la fabricación de patrones litográficos 2D a partir de las láminas delgadas y las nanoestructuras soportadas. La investigación se contempla con estudios básicos encaminados al desarrollo de procesos de “patterning químico” basados en procesos de funcionalización superficial mediante plasmas y de derivatización química de monocapas autoensambladas. Tanto la metodología sintética mediante plasmas remotos como los procesos de microstructuración son totalmente compatibles con la tecnología optoelectrónica actual y la tecnología microelectrónica. Ambos procesos, por tanto, pueden llevarse a cabo a escala de oblea de silicio (wafer scale) y escalarse a procesos de fabricación industrial efectivos. Estos materiales y procesos se emplearán en la fabricación de dos tipos de dispositivos a escala de prototipo como son: los sensores de gases fotónicos y las microestructuras luminiscentes para aplicaciones de marcado inteligente. Los sensores de gases consistirán en una lámina o estructura luminiscente integrada en un cristal fotónico 1D diseñados de acuerdo a las propiedades ópticas y la longitud de onda de la emisión luminiscente de la capa sensora correspondiente. Los dispositivos de marcado inteligente consistirán en patrones litográficos complejos construidos a partir de láminas o multicapas luminiscentes con funcionalidades específicas e, incluso, respuesta ambiental o sensora no desarrollada por ninguna otra tecnología hasta la fecha.


Sistemas para la Detección de Explosivos en Infraestructuras Públicas



Investigador Principal: Angel Barranco Quero
Periodo: 1-09-2010 / 31-10-2011
Organismo Financiador: Ministerio de Industria (Contrato: ARQUIMEA)
Código: Centro para el Desarrollo Tecnológico Industrial (Programa CENIT)
Componentes: Francisco Javier Aparicio, Agustín R. González-Elipe, Ana Isabel Borrás Martos, Juan Pedro Espinós

Resumen [+]

El objetivo de este proyecto es el desarrollo de láminas delgadas con propiedades ópticas adecuadas como elementos activos en sensores ópticos capaces de responder a la presencia de gases y/o productos volátiles procedentes de la descomposición parcial de explosivos.


Desarrollo de membranas de regeneración ósea guiada modificadas a escala nanométrica (OSTEOMEM)



Investigador Principal: Agustín R. González-Elipe
Periodo: 03-02-2010 / 02-02-2013
Organismo Financiador: Junta de Andalucía
Código: P09-CTS-5189 (Proyecto de Excelencia)
Componentes: José Cotrino Bautista, Rafael Alvarez Molina, Carmen López Santos, Jorge Gil Rostra, Antonia Terriza Fernández

Resumen [+]

OSTEOMEM persigue el desarrollo de membranas de regeneración ósea reabsorbibles y biodegradables de base polimérica para su uso en cirugía oral y maxilofacial para el tratamiento de defectos óseos. Durante la curación de estos, las membranas deben preservar la aparición de tejidos blandos en los mismos propiciando que la regeneración del hueso ocupe el defecto, dejando tras la reabsorción de la membrana una estructura de tejidos análoga a la que existía antes de la intervención quirúrgica. Este efecto se basa fundamentalmente en un mecanismo de barrera con membranas que se degradan en el interior del cuerpo en un periodo de cuatro a seis meses, evitando la segunda cirugía que generalmente se requiere para retirar membranas no biodegradables. Se espera que las membranas desarrolladas en el proyecto permitan alcanzar los resultados clínicos de las membranas de regeneración animal evitando los problemas asociados a su origen.


Nanopartículas funcionalizadas para aplicaciones de hipertermia y evaluación de su ecotoxicidad



Investigador Principal: Asunción Fernández Camacho
Periodo: 03-02-2010 / 02-02-2013
Organismo Financiador: Junta de Andalucía
Código: P09-FQM-4554
Componentes: J. Blasco, M. Hampel, Carlos López, L.M. Lubián, I. Moreno, Miguel Angel Muñoz, David Philippon, T. Cristina Rojas, Inmaculada Rosa, Carlos García-Negrete

Resumen [+]

En este Proyecto de Excelencia se parte de la experiencia previa del grupo TEP-217 en el desarrollo y caracterización de nanopartículas funcionalizadas potencialmente biocompatibles y se pretende avanzar en cuatro direcciones. a) Continuar con el desarrollo de nanopartículas basadas principalmente en Au, Ag y óxidos magnéticos con distintas funcionalizaciones y microestructura. b) Profundizar en la fisico-química de su interacción con campos electromagnéticos (en un amplio rango de frecuencias desde kHz a GHz) para producir calentamientos localizados. Actualmente se han propuesto distintos mecanismos (corrientes inducidas, histéresis, relajación de momentos magnéticos y movimiento browniano) sin que existan todavía suficientes datos para comprender e interpretar los resultados experimentales. c) Establecer una colaboración multidisciplinar con el grupo RNM-306, especialista en ensayos de ecotoxicidad, que permita mejorar el conocimiento del impacto ambiental de las nanopartículas (principalmente de oro y plata) en los ecosistemas marinos, que son el sumidero final de una buena parte de los nanomateriales producidos en la actualidad. d) Realizar estudios preliminares de la toxicidad de las nanopartículas en función del campo electromagnético aplicado. En cualquier proyecto dedicado a la nanotecnología resulta extremadamente valioso introducir estudios que nos permitan determinar el impacto toxicológico y ambiental de los nuevos materiales que se están desarrollando en la actualidad.

Un objetivo fundamental de este proyecto es la formación de personal investigador a través de la realización de una Tesis Doctoral en el Instituto de Ciencia de Materiales de Sevilla.


Materiales mesoporosos (HA-SBA-15) funcionalizados con una proteína rhBMP-2 con afinidad por colágeno y sus estructuras híbridas con colágeno para ingeniería del tejido óseo



Investigador Principal: M. Aránzazu Díaz Cuenca
Periodo: 01-01-2010 / 31-12- 2012
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: BIO2009-13903-C02-02
Componentes: M. Lourdes Ramiro Gutiérrez

Resumen [+]

Los materiales soporte denominados biomateriales, matrices, armazones, andamiajes tisulares o scaffold son uno de los elementos básicos para la fabricación de nuevos tejidos artificiales. El biomaterial sirve de soporte para las interacciones celulares y para la formación de matriz extracelular (ECM). Entre los distintos tipos de materiales que se emplean naturales o sintéticos, las cerámicas bioactivas con base de sílice en el sistema ternario SiO2-CaO-P2O5 han mostrado excelente propiedades para su aplicación en cirugía ortopédica reparadora y regeneradora. Por otra parte el desarrollo de nuevas rutas de síntesis que combinan la química sol-gel y el autoensamblado de moléculas (polímeros) directoras o formadoras de estructura ofrece grandes posibilidades para la síntesis de de nuevos materiales bioactivos organizados a escala nanométrica con alta superficie y reactividades mejoradas. Trabajo previo de la IP de esta solicitud ha resultado en la síntesis de un nuevo biomaterial nanocomposite (HA-SBA-15) biocompatible constituido por nanopartículas de hidroxiapatito de calcio en asociación con la matriz de sílice mesoestructurada. Además de la biocompatibilidad, la alta superficie y la distribución de poros con un tamaño homogéneo hacen que este material sea un candidato muy interesante para su utilización como matriz para la adsorción de moléculas terapéuticas, medicamentos o factores de crecimiento que requieran su liberación de forma controlada. Las proteínas morfogenéticas de hueso (BMPs) han sido utilizadas ampliamente debido a sus propiedades osteoinductoras. Las proteínas recombinantes BMP-2 y BMP-7 han sido aprobadas por la FDA para su uso en cirugía ortopédica, sin embargo, el uso de estos factores de crecimiento no está muy extendido debido al alto costo de estos tratamientos y al miedo a posibles efectos secundarios como consecuencia de su utilización en altas concentraciones sin un sistema de liberación adecuado. Por otra parte resultados recientes del equipo coordinador de esta solicitud (subproyecto 2) ha producido y patentado una proteína recombinante BMP (rh-BMP-2) con un dominio de unión al colágeno tipo I (CBD). Esta proteína de fusión ha mostrado ventajas respecto a la proteína nativa BMP-2 y su uso combinado con colágeno puede representar una alternativa terapéutica mejor y más segura en la reparación del tejido óseo. En este subproyecto se propone el estudio de nuevas rutas de síntesis para producir un material nano-organizado (HA-SBA-15) con variaciones en los parámetros texturales y las nanopartículas de HA con el objetivo de optimizar las propiedades de adsorción y posterior liberación de la proteína rhBMP-2 con afinidad por colágeno. Un objetivo paralelo será determinar las variables y condiciones experimentales adecuadas para incorporar la proteína rhBMP-2-CBD al material nano-organizado. El estudio analizará la cantidad de biomolécula, la cinética de desorción y su integridad. Una segunda tarea de esta propuesta es la consolidación del material particulado nano-organizado en piezas tridimensionales híbridas de material cerámico-colágeno biocompatibles, macroporosas y con una estabilidad mecánica mínima que permita su utilización en los experimentos in vivo que se proponen llevar a cabo como parte de las tareas del Subproyecto 2. Se ensayaran métodos para obtener piezas tridimensionales que conserven sus características nanoestructuradas. Se abordará la integración del material sin funcionalizar y funcionalizado con rhBMP-2-CBD.


Materiales poliméricos y nanocomposites híbridos en forma de lámina delgada para aplicaciones fotónicas y fotovoltaicas (NANOPHOTON)



Investigador Principal: Angel Barranco Quero
Periodo: 01-01-2010 / 02-02-2013
Organismo Financiador: Junta de Andalucía
Código: P09-TEP-5283 (Proyecto de Excelencia)
Componentes: Ana Borrás, Fabián Frutos, Lola González-García, Said Hamad, S. Lago, Alberto Palmero, Carmen Ruiz-Herrero, Juan R. Sánchez-Valencia, Johan Toudert

Resumen [+]

El proyecto NANOPHOTON persigue el desarrollo de una nueva familia de materiales, estructuras y prototipos de dispositivos con aplicación en campos tales como el aprovecha-miento de energía solar, el análisis medioambiental y la tecnología espacial. El punto de parti-da del proyecto es la investigación en nuevos materiales ópticamente activos en forma de película delgada nanométrica de carácter polimérico e híbrido. Estas láminas delgadas activas se procesarán e integrarán usando diferentes técnicas para formar estructuras ópticas de uso como sensores fotónicos ambientales, filtros fotónicos insensibles al ángulo de incidencia para comunicaciones en satélites y celdas fotovoltaicas. Un aspecto muy interesante del proyecto es su completa compatibilidad con los métodos sintéticos de uso común en tecnología microelectrónica y optoelectrónica siendo fácilmente transferibles a la industria. NANOPHOTON integra desde estudios fundamentales de simulación molecular a procesos de fabricación de estructuras nanométricas con actividad fotónica pasando por la fabricación de estructuras y prototipos para llegar a test de validación de prototipos en condiciones reales.


Papel de los aditivos en los sistemas composites de hidruros metálicos reactivos para almacenamiento de hidrógeno



Investigador Principal: Asunción Fernández Camacho
Periodo: 01/01/2010 - 31/12/2012
Organismo Financiador: Ministerio de Educación y Ciencia
Código: CTQ2009-13440
Componentes: Carlos López, Cristina Rojas Ruiz, Gisela Arzac, Dirk Hufschmidt, Raimondo Ceccini, Emilie Deprez

Resumen [+]

Dada la problemática actual por el agotamiento a corto-medio plazo de los combusti-bles fósiles y los cambios climáticos causados por el efecto invernadero, se hace necesaria la reconsideración de una política energética global. El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo por tratarse de una alternativa viable y limpia. En el presente proyecto se propone el estudio de los llamados sistemas composites de hidruros reactivos (RHC) para almacenamiento de hidrógeno. Estos sistemas se basan en acoplar un hidruro metálico sencillo (i.e. MgH2) con un hidruro complejo (típicamente un compuesto borohidruro, i.e LiBH4) para dar una reacción reversible que produce o consume hidrógeno. El sistema puede así usarse como material para almacenamiento de hidrógeno de acuerdo a la siguiente reacción: MgH2+2LiBH4 ↔ MgB2+LiH+4H2 (11.4 wt% capacidad de almacenamiento de hidrógeno). La reacción mejora el balance de calor, en comparación con el MgH2 puro, al reducir la liberación de calor durante el proceso de carga. Para mejorar los aspectos cinéticos (reducción de las temperaturas y tiempos de operación) se ha propuesto el uso de catalizadores y/o aditivos. El principal objetivo del proyecto es comprender el papel de estos aditivos para mejorar las cinéticas de sorción de hidrógeno. En particular se han seleccionado como aditivos para este estudio los productos comerciales Ti-Isopropoxide (TiO4C12H28), TiO2 y VCl3 . También se prepararan en nuestro laboratorio otros catalizadores como Co3B, Ni3B o RuCo que igualmente se ensayarán. Los sistemas se prepararán y activarán por molienda de alta energía de los dos mate-riales hidruros molidos juntos con ó sin aditivos (5-10 mol%). Los estudios cinéticos se llevarán a cabo a través de medidas de sorción gravimétrica y volumétrica de hidrógeno (desorción o absorción vs. tiempo a T constante) y de la calorimetría de barrido diferencial (DSC). Se llevará también a cabo un estudio exhaustivo de caracterización microestructural y química de los sistemas en las diferentes etapas (tras la molienda, desorbidos y re-absorbidos) con las si-guientes técnicas: Difracción de rayos X (XRD), microscopía electrónica de transmisión (TEM) acoplada al análisis EDX (energía dispersiva de rayos X) y EELS (espectroscopía de pérdida de energía de electrones), espectroscopía de fotoemisión (XPS) y espectroscopía de absorción de rayos X (XAS). El estudio comparativo de las muestras con y sin aditivos y la correlación entre los estudios cinéticos y el análisis microestructural y químico, deben clarificar el mecanismo de la mejora cinética producida por los aditivos. Estos mecanismos están a día de hoy lejos de ser comprendidos. Sobre la base del conocimiento adquirido se espera mejorar de manera significativa estos sistemas en relación a sus aplicaciones para almacenamiento de hidrógeno.


Estudio de Materiales modificados superficialmente mediante Reflexafs SURCOXAFS



Investigador Principal: Adela Muñoz Páez
Periodo: 01-01-2009 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2008-06652
Componentes: Stuart Ansell, Regla Ayala Espinar, Sofía Díaz Moreno, Lola González García, José Manuel Martínez Fernández, Víctor López Flores

Resumen [+]

La espectroscopia de Absorción de Rayos X en modo reflexión, ReflEXAFS, es una técnica novedosa que proporciona la información característica del EXAFS, estructura del entorno local del elemento absorbente, junto con la obtenida por medidas de reflectometría, tales como rugosidad, espesor de capa o densidad. Todo ello focalizado en la zona próxima a la superficie, proporcionando además la posibilidad de controlar el espesor analizado en función del ángulo de incidencia del haz, en el rango de 20 a 200 Ǻ. Asimismo, y a diferencia de otras espectroscopias superficiales como XPS, permite acceder a capas “enterradas”. Por ello es muy útil para el estudio de materiales con propiedades singulares en su superficie, tales como los modificados superficialmente y los obtenidos por deposición de capas finas. Habiendo desarrollando los protocolos de medida en proyectos previos, se propone la aplicación de la técnica a sistemas reales de dos tipos: aceros modificados superficialmente mediante nitruración y materiales formados por capas finas mixtas con propiedades ópticas y magnéticas singulares. Aparte del interés intrínseco de la técnica y de los sistemas objeto de estudio, este proyecto tiene relevancia en el marco del desarrollo de la espectroscopia XAS en relación con la línea española del ESRF, SPLINE, y de la nueva fuente española de radiación sincrotrón ALBA.


Funcionalización superficial de materiales para aplicaciones de alto valor añadido (FUNCOAT)



Investigador Principal: Agustín R. González-Elipe
Periodo: 15-12-2008 / 15-12-2013
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: CSD2008- 00023 (Consolider)
Componentes: Fernández Camacho, A., Espinós, J.P., Yubero, F., Cotrino, J., Sánchez López, J.C., Barranco, A., Palmero, A., Rojas, C.

Resumen [+]

FUNCOAT es un proyecto integrado dentro de la convocatoria CONSOLIDER-INGENIO 2010 que persigue explotar las sinergias existentes entre la comunidad científica española en materiales, teniendo como objetivo general el desarrollo de nuevos métodos y la optimización de procedimientos de funcionalización superficial de materiales para la mejora de sus propiedades. El proyecto integra a 14 centros de investigación diferentes, que cubren desde aspectos básicos y teóricos hasta diversas aplicaciones finales. Esta integración de esfuerzos es crítica para lograr avances sustanciales en este campo, más allá que la mera acumulación de resultados. Los grupos de investigación pertenecen a diversas Universidades, CSIC (organismo que actúa como gestor del proyecto) y centros tecnológicos, y presentan relaciones científicas que, en algunos casos, se remontan hasta hace 15 años. Objetivos científico-técnicos parciales son: la comprensión de los fenómenos fundamentales que rigen la modificación de superficies y crecimiento de capas, el control micro y nanoestructural de superficies y capas delgadas, la optimización de los procesos de crecimiento de las capas, la obtención de superficies modificadas con características multifuncionales con aplicaciones en diversos campos (protección mecánica, óptica, magnetismo, biomateriales, energía, etc) y, finalmente, el desarrollo de nuevos dispositivos y aplicaciones de los materiales funcionales en sectores tecnológicos clave. Otros objetivos horizontales, relacionados con los anteriores, son la formación de investigadores en técnicas y métodos de funcionalización y el desarrollo de una transferencia tecnológica eficaz a los sectores productivos. Sectores estratégicos clave en los que las actividades de FUNCOAT inciden con mayor impacto son la metalurgia, vidrio, plásticos, sensores, salud y energía. El proyecto se estructura en torno a los ejes de actividad siguientes que deben permitir la mejor coordinación de los esfuerzos y la integración de las distintas actividades de los grupos. A) Fenómenos básicos de superficies, intercaras y láminas delgadas, B) Nuevos procesos para el control de la micro- y nano- estructura superficiales, C) Recubrimientos mecánicos y metalúrgicos para protección superficial, D) Funcionalización química de superficies y aplicaciones biomédicas, E) Recubrimientos para aplicaciones ópticas y control eficiente de captación energía solar, F) Nuevos fenómenos magnéticos en superficies e interfases.


Desarrollo y diseminación de nuevas técnicas de caracterización nanomecánica y standars



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-09-2008 / 31-08-2011
Organismo Financiador: Unión Europea
Código: NMP3-CA-2008-218659
Componentes: Godinho, V., Philippon, D.

Resumen [+]

El proyecto se dedica al desarrollo, mejora, y standarización de las técnicas de caracterización, los métodos y los equipos en los ensayos nano-mecánicos. Las actividades a nivel Europeo, coordinadas por un centro virtual, mejorarán la metrología de nanoindentación actual y permitirán un conocimiento más profundo de la relación estructura-propiedades en la nano-escala. Estos métodos son una herramienta única para caracterizar el comportamiento mecánico en la nanoescala de nanocomposites, nanocapas e interfases. Este trabajo también producirá una base sólida para definer y preparer nuevos standards que soporten la metodología de caracterización de los nanomateriales. Las etapas incluyen el desarrollo de los métodos clásicos de nanoindentación dinámica y su aplicación a campos nuevos como el rayado y las medidas de desgaste y la aplicación de nano-indentadores modificados. También se trabajará en la determinación uniforme de los parámetros instrumentals y en la definición de standards par alas nuevas aplicaciones. El centro virtual diseminará la información sobre la base de una nueva "base de datos para la caracterización Nano-mecánica". Esto se conseguirá a través de los trabajos de "round robin" entre los socios é incluirá igualmente datos de de otras fuentes de investigación y la búsqueda bibliográfica.


Plasmas de nitrógeno para funcionalizacion superficial de materiales (PLASNITRO)



Investigador Principal: José Cotrino Bautista
Periodo: 01-02-2008 / 31-01- 2011
Organismo Financiador: Junta de Andalucía
Código: P07-FQM-03298 (Proyecto de Excelencia)
Componentes: Agustín R. González-Elipe, Francisco Yubero Valencia

Resumen [+]

En el proyecto PlasNitro se aborda la caracterización de plasmas de nitrógeno en di-versas aplicaciones tecnológicas relacionadas con técnicas de deposición y funcionalización de materiales, reformado y procesos de esterilización que involucran a la Tecnología de Plasma. Se pondrán a punto diferentes procedimientos para medir propiedades de los plasmas, usados en dopado, deposición, funcionalización y modificación de materiales, que contienen nitrógeno usando técnicas de diagnosis basadas en la detección de especies de nitrógeno. El nitrógeno es hoy día un componente usual, sólo o en mezclas con otros gases, en muchos procesos usados en tecnología de plasma. Su caracterización experimental y/o teórica permitirá obtener propiedades fundamentales del plasma (densidad electrónica, temperatura electrónica, temperatura del gas, especies reactivas, etc.) y conocer la contribución a las reacciones homogéneas (en fase plasma) y heterogéneas (interacción plasma-superficie) de los componentes procedentes del nitrógeno. En el proyecto se elaborarán códigos numéricos para obtener la función de distribución electrónica en el plasma. Para este fin será necesaria previamente la evaluación de la distribución vibracional del nitrógeno. Este paso implica tener en cuenta múltiples procesos vibracionales-vibracionales, vibracionales-traslacionales y vibracionales-rotacionales. A partir de la función de distribución electrónica se podrán construir modelos de fluido del plasma en los que intervienen las especies más importantes. Los cálculos teóricos se complementarán con medidas experimentales usando sonda electrostática de Langmuir, que permitirán medir la función de distribución electrónica, así como densidad y temperatura de los electrones. Mediante un analizador de gases residuales se controlará la presión parcial de nitrógeno en cada aplicación y los componentes neutros del plasma. Los modelos cinéticos del plasma de nitrógeno permitirá en muchos casos la interpretación de medidas en el plasma alejado del equilibrio termodinámico y las técnicas de escalado dinámico y simulación Monte Carlo permitirán el control de la nano/microestructura de los materiales depositados/modificados. Se tendrán, de esta forma, técnicas que permitirán controlar y mejorar los procedimientos de trabajo y las propiedades deseadas en los materiales.


Recubrimientos nanoestructurados multifuncionales para aplicaciones mecánicas y tribológicas (NANOMETRIB)



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-10-2007 / 30-09-2011
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2007-66881-C02-01
Componentes: Asunción Fernández Camacho, Cristina Fernández, Miguel Angel Muñoz-Márquez, Said El Mrabet, Vanda Godinho, M. David Abad

Resumen [+]

En el campo de las aplicaciones mecánicas y tribológicas, las investigaciones se dirigen al desarrollo de nuevos sistemas que consigan aumentar la eficiencia de operaciones industriales, equipos o herramientas mediante el incremento de la dureza, la reducción de la fricción y la velocidad del desgaste de los materiales en contacto o la resistencia a la oxidación. Estas mejoras suponen un ingente ahorro económico y energético al alargar la vida media de los materiales sin necesidad de su reparación o cambio, como también, una reducción del empleo de emulsiones lubricantes con aceites o grasas. Este proyecto se propone el desarrollo de nuevos recubrimientos nanoestructurados multifuncionales por la técnica de PVD-Magnetron Sputtering para aplicaciones mecánicas y tribológicas en los que se alcance un equilibrado compromiso entre todas las propiedades mencionadas de fricción, dureza, estabilidad térmica. La combinación de múltiples funciones en un mismo material dota de un extraordinario valor añadido al sistema. Para lograr este objetivo general se van a preparar recubrimientos caracterizados donde el tamaño y distribución de las fases componentes, la composición química y su microestructura estén confinados en el rango nanométrico. Los sistemas elegidos comprenden cristales de materiales duros (nitruros, carburos o boruros de metales de transición: Cr, Ti, W) que pueden estar rodeados de una segunda fase que actúe como lubricante a base de C o dicalcogenuros de W) y dopados con ciertos metales para incrementar su resistencia térmica (V ó Nb). En todos los casos, el proyecto comprende su síntesis, caracterización estructural y química, así como su validación práctica en ensayos mecánicos y tribológicos. El estudio de la relación existente entre la microestructura y las propiedades medidas será un objetivo esencial puesto que permitirá una mayor comprensión de los mecanismos de actuación, y por ende, la optimización de tales sistemas nanoestructurados para su mejor aprovechamiento tecnológico.




2018


Room temperature synthesis of water-dispersible Ln(3+):CeF3 (Ln = Nd, Tb) nanoparticles with different morphology as bimodal probes for fluorescence and CT imaging


Gonzalez-Mancebo, D; Becerro, AI; Rojas, TC; Olivencia, A; Corral, A; Balcerzyk, M; Cantelar, E; Cusso, F; Ocana, M
Journal of Colloid and Interface Science, 520 (2018) 134-144

ABSTRACT

The singular properties of lanthanide-based inorganic nanoparticles (NPs) has raised the attention of the scientific community in biotechnological applications. In particular, those systems with two or more functionalities are especially interesting. In this work, an effective and commercially attractive procedure has been developed that renders uniform, water-dispersible Ln(3+):CeF3 (Ln = Tb, Nd) NPs with different shapes and size. The method consists of the homogeneous precipitation, in a mixture of polyol and water, of cations and anions using precursors that allow the controlled release of the latter. The advantages of the reported method are related to the absence of surfactants, dispersing agents or corrosive precursors as well as to the room temperature of the process. The obtained Tb:CeF3 NPs produce an intense emission after excitation through the Ce-Tb energy transfer band located in the UV spectral region, thus being potentially useful as phosphors for in-vitro imaging purposes. On the other hand, the synthesized Nd:CeF3 NPs are good candidates for in-vivo imaging because their excitation and emission wavelengths lie in the biological windows. Finally, the excellent X-ray attenuation efficacy of the Nd:CeF(3)NPs is shown, which confers double functionality to this material as both luminescence bioprobe and contrast agent for X-ray computed-tomography. 


Junio, 2018 | DOI: 10.1016/j.jcis.2018.03.007

Strong activation effect on a ru-co-c thin film catalyst for the hydrolysis of sodium borohydride


Arzac, GM; Paladini, M; Godinho, V; Beltran, AM; de Haro, MCJ; Fernandez, A
Scientific Reports, 8 (2018) art. 9755

ABSTRACT

In this work, we prepared a series of Ni foam supported Ru-Co, Ru-Co-B and Ru-Co-C catalysts in the form of columnar thin films by magnetron sputtering for the hydrolysis of sodium borohydride. We studied the activity and durability upon cycling. We found a strong activation effect for the Ru-Co-C sample which was the highest ever reported. This catalyst reached in the second cycle an activity 5 times higher than the initial (maximum activity 9310 ml.min(-1).g(CoRu)(-1) at 25 degrees C). Catalytic studies and characterization of the fresh and used samples permitted to attribute the strong activation effect to the following factors: (i) small column width and amorphous character (ii) the presence of Ru and (iii) dry state before each cycle. The presence of boron in the initial composition is detrimental to the durability. Our studies point out to the idea that after the first cycle the activity is controlled by surface Ru, which is the most active of the two metals. Apart from the activation effect, we found that catalysts deactivated in further cycles. We ascribed this effect to the loss of cobalt in the form of hydroxides, showing that deactivation was controlled by the chemistry of Co, the major surface metal component of the alloy. Alloying with Ru is beneficial for the activity but not for the durability, and this should be improved.


Junio, 2018 | DOI: 10.1038/s41598-018-28032-6

Growth of nanocolumnar porous TiO2 thin films by magnetron sputtering using particle collimators


Garcia-Valenzuela, A; Alvarez, R; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Surface & Coatings Technology, 343 (2018) 172-177

ABSTRACT

The selective incorporation of deposition species with preferential directionality is analyzed during the growth of TiO2 thin films by magnetron sputtering. Using wisely-designed collimators, tilted nanocolumnar morphologies are grown in a ballistic deposition regime, i.e. when most deposition species arrive at the film surface along well-defined preferential directions, and also in a thermalized deposition regime, when these species follow an isotropic momentum distribution in the plasma gas. The obtained results suggest that the use of particle collimators may promote the growth of porous thin films even in the classical magnetron sputtering configuration, when the target and the substrate are parallel. General insights are given on this approach and, as a proof of concept, its principles applied for the synthesis of nanostructured films in a laboratory-size reactor.


Junio, 2018 | DOI: 10.1016/j.surfcoat.2017.09.039

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics


Manuel, JM; Jimenez, JJ; Morales, FM; Lacroix, B; Santos, AJ; Garcia, R; Blanco, E; Dominguez, M; Ramirez, M; Beltran, AM; Alexandrov, D; Tot, J; Dubreuil, R; Videkov, V; Andreev, S; Tzaneva, B; Bartsch, H; Breiling, J; Pezoldt, J; Fischer, M; Muller, J
Scientific Reports, 8 (2018) art. 6879

ABSTRACT

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.


Mayo, 2018 | DOI: 10.1038/s41598-018-25416-6

In Vitro Comparative Study of Oxygen Plasma Treated Poly(Lactic-Co-Glycolic) (PLGA) Membranes and Supported Nanostructured Oxides for Guided Bone Regeneration Processes


Torres-Lagares, D; Castellanos-Cosano, L; Serrera-Figallo, MA; Lopez-Santos, C; Barranco, A; Rodriguez-Gonzalez-Elipe, A; Gutierrez-Perez, JL
Materials, 11 (2018) art. 752

ABSTRACT

(1) Background: The use of physical barriers to prevent the invasion of gingival and connective tissue cells into bone cavities during the healing process is called guided bone regeneration. The objective of this in-vitro study was to compare the growth of human osteoblasts on Poly(Lactic-co-Glycolic) (PLGA) membranes modified with oxygen plasma and Hydroxyapatite (HA), silicon dioxide (SiO2), and titanium dioxide (TiO2) composite nanoparticles, respectively. (2) Methods: All the membranes received a common treatment with oxygen plasma and were subsequently treated with HA nanostructured coatings (n = 10), SiO2 (n = 10) and TiO2 (n = 10), respectively and a PLGA control membrane (n = 10). The assays were performed using the human osteoblast line MG-63 acquired from the Center for Scientific Instrumentation (CIC) from the University of Granada. The cell adhesion and the viability of the osteoblasts were analyzed by means of light-field microphotographs of each condition with the inverted microscope Axio Observer A1 (Carl Zeiss). For the determination of the mitochondrial energy balance, the MitoProbe (TM) JC-1 Assay Kit was employed. For the determination of cell growth and the morphology of adherent osteoblasts, two techniques were employed: staining with phalloidin-TRITC and staining with DAPI. (3) Results: The modified membranes that show osteoblasts with a morphology more similar to the control osteoblasts follow the order: PLGA/PO2/HA > PLGA/PO2/SiO2 > PLGA/PO2/TiO2 > PLGA (p < 0.05). When analysing the cell viability, a higher percentage of viable cells bound to the membranes was observed as follows: PLGA/PO2/SiO2 > PLGA/PO2/HA > PLGA/PO2/TiO2 > PLGA (p < 0.05), with a better energy balance of the cells adhered to the membranes PLGA/PO2/HA and PLGA/PO2/SiO2. (4) Conclusion: The membrane in which osteoblasts show characteristics more similar to the control osteoblasts is the PLGA/PO2/HA, followed by the PLGA/PO2/SiO2.


Mayo, 2018 | DOI: 10.3390/ma11050752

The nanostructure of porous cobalt coatings deposited by magnetron sputtering in helium atmosphere


Lacroix, B; Godinho, V; Fernandez, A
Micron, 108 (2018) 49-54

ABSTRACT

In this work, (scanning) transmission electron microscopy has been used to study the nanostructure of porous cobalt coatings obtained by magnetron sputtering using helium as process gas. This nanostructure consists of closed pores of different nanometric size (about 4-20 nm) that are distributed all over a nanocrystalline Co matrix and filled with the deposition gas. Spatially resolved electron energy-loss spectroscopy analysis was applied to measure and map, with high lateral resolution, the relevant physical properties (density, pressure and He-K edge shift) of helium trapped inside these individual nanopores, in order to provide new insights about the growth mechanism involved in such systems. In particular, a coefficient of proportionality, C = 0.039 eV nm(3), between the blue shift of the He K-edge and the He density has been found. In addition, very high He densities (10-100 at./nm(3)) and pressures in the gigapascal range (0.05-5.0 GPa) have been measured. The linear dependence of these parameters as a function of the inverse radii obeying to the Laplace-Young law for most of the pores suggests that their formation during the coating's growth takes place in regime of elastic deformation of the Co matrix.


Mayo, 2018 | DOI: 10.1016/j.micron.2018.02.004

Microemulsion Assisted Sol-Gel Method as Approach to Load a Model Anticancer Drug inside Silica Nanoparticles for Controlled Release Applications


Jaramillo, N; Paucar, C; Fernandez, A; Negrete, CG; Garcia, C
Collid and Interface Science Communications, 24 (2018) 13-17

ABSTRACT

Silica nanoparticles are attractive carriers due to their improved safety and effectiveness in drug delivery. Silica nanoparticles were synthesized by using microemulsion assisted sol-gel method, and a model anticancer drug 5-fluorouracil (5-FU) was added to the silica precursor before hydrolysis and condensation reactions start. The obtained materials were characterized by Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). Drug encapsulation within silica nanoparticles causes an increase in particle size. However, particle morphology is not affected. The drug release profile was obtained through high performance liquid chromatography (HPLC). The encapsulation approach showed to be effective for sustaining a continuous and increasing release during testing time (98 h). Further studies were performed to evaluate the cytotoxic effects of silica nanoparticles with loaded 5-FU on Chinese hamster ovary cells (CHO-K1). Materials are non-cytotoxic for all concentration tested (5-200 mu g/mL).


Mayo, 2018 | DOI: 10.1016/j.colcom.2018.03.002

Enhancing Moisture and Water Resistance in Perovskite Solar Cells by Encapsulation with Ultrathin Plasma Polymers


Idigoras, J; Aparicio, FJ; Contreras-Bemal, L; Ramos-Terron, S; Alcaire, M; Sanchez-Valencia, JR; Borras, A; Barranco, A; Anta, JA
ACS Applied Materials & Interfaces, 10 (2018) 11587-11594

ABSTRACT

A compromise between high power conversion efficiency and long-term stability of hybrid organic inorganic metal halide perovskite solar cells is necessary for their outdoor photovoltaic application and commercialization. Herein, a method to improve the stability of perovskite solar cells under water and moisture exposure consisting of the encapsulation of the cell with an ultrathin plasma polymer is reported. The deposition of the polymer is carried out at room temperature by the remote plasma vacuum deposition of adamantane powder. This encapsulation method does not affect the photovoltaic performance of the tested devices and is virtually compatible with any device configuration independent of the chemical composition. After 30 days under ambient conditions with a relative humidity (RH) in the range of 35-60%, the absorbance of encapsulated perovskite films remains practically unaltered. The deterioration in the photovoltaic performance of the corresponding encapsulated devices also becomes significantly delayed with respect to devices without encapsulation when vented continuously with very humid air (RH > 85%). More impressively, when encapsulated solar devices were immersed in liquid water, the photovoltaic performance was not affected at least within the first 60 s. In fact, it has been possible to measure the power conversion efficiency of encapsulated devices under operation in water. The proposed method opens up a new promising strategy to develop stable photovoltaic and photocatalytic perovskite devices.


Abril, 2018 | DOI: 10.1021/acsami.7b17824

Electrophoretic deposition of mixed copper oxide/GO as cathode and N-doped GO as anode for electrochemical energy storage


Jafari, EA; Moradi, M; Hajati, S; Kiani, MA; Espinos, JP
Electrochimica Acta, 268 (2018) 392-402

ABSTRACT

In this work, energy storage properties of mixed copper oxide wrapped by reduced graphene oxide and nitrogen-doped reduced graphene oxide were investigated. First, co-electrophoretic deposition technique was used to coat GO@CuO on nickel foam; followed by electrochemical phase transformation to rGO@CuxO. Electron spectroscopy analyses (XPS, REELS and UPS) confirm the phase transformation and electrochemical reduction. Then, an electrophoretic deposition was carried out for coating nitrogen-doped graphene oxide on nickel foam coupled to its electrochemical reduction to the NrGO. The cathode and anode performances were studied by galvanostatic charge-discharge, cyclic voltammetry and impedance spectroscopy. The rGO@CuxO and NrGO exhibit a favorable specific capacity of 267.2 and 332.6 C g(-1) at 2 A g(-1), respectively. High electrochemical activity and elimination of polymer binders with a maximum potential of 1.6 V are among the advantages of rGO@CuxO//NrGO electrochemical charge storage device. Furthermore, fabricated device provided a maximum specific power and specific energy of 11917.24 W kg(-1) and 14.15 Wh kg(-1), respectively, with 86% capacity retention after 2000 cycles.


Abril, 2018 | DOI: 10.1016/j.electacta.2018.02.122

Colorimetric energy sensitive scintillator detectors based on luminescent multilayer designs


Ferrer, FJ; Gil-Rostra, J; Gonzalez-Elipe, AR; Yubero, F
Sensors and Actuators A-Physical, 272 (2018) 217-222

ABSTRACT

In this work we present a new concept for energy sensitive radiation-beam scintillator detectors based on a luminescent multilayer design, where each layer within the stack consists of a rare-earth-doped highly transparent oxide. For a given type of particle beam (i.e., protons, a particles, etc.), its penetration depth, and therefore its energy loss at a particular buried layer, depends on its initial kinetic energy. Relying on this principle and since the intensity of the luminescent response of each layer and substrate should be proportional to the energy deposited by the radiation beam, we prove that a characteristic energy dependent color emission is obtained depending on both the phosphors integrated in the luminescent stack and on the primary energy and type of particle beam. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters to achieve a broad gamut in colorimetric response. The developed scintillators are designed to operate in a transmission geometry (light detection from the opposite side of the incident radiation) which is well suited for high energy particle detection in fields such as oncotherapy, space radiation, or of fusion studies. The principles of the method are illustrated with a case example typical of ion beam accelerators devoted to materials analysis. It is obtained that the kinetic energy of protons/alpha particle beams can be distinguished and evaluated with a sensitivity of 0.06/0.25 chromaticity units per MeV in the 0.7-2.0 MeV range. 


Abril, 2018 | DOI: 10.1016/j.sna.2018.01.062

Dye Giant Absorption and Light Confinement Effects in Porous Bragg Microcavities


Oliva-Ramirez, M; Gil-Rostra, J; Simonsen, AC; Yubero, F; Gonzalez-Elipe, AR
ACS Photonics, 5 (2018) 984-991

ABSTRACT

This work presents a simple experimental procedure to probe light confinement effects in photonic structures. Two types of porous 1D Bragg microcavities with two resonant peaks in the reflection gap were prepared by physical vapor deposition at oblique angle configurations and then infiltrated with dye solutions of increasing concentrations. The unusual position shift and intensity drop of the transmitted resonant peak observed when it was scanned through the dye absorption band have been accounted for by the effect of the light trapped at their optical defect layer. An experimentally observed giant absorption of the dye molecules and a strong anomalous dispersion in the refractive index of the solution are claimed as the reasons for the observed variations in the Bragg microcavity resonant feature. Determining the giant absorption of infiltrated dye solutions is proposed as a general and simple methodology to experimentally assess light trapping effects in porous photonic structures.


Marzo, 2018 | DOI: 10.1021/acsphotonics.7b01283

Copper-containing mesoporous bioactive glass promotes angiogenesis in an in vivo zebrafish model


Romero-Sanchez, LB; Mari-Beffa, M; Carrillo, P; Medina, MA; Diaz-Cuenca, A
Acta Biomaterialia, 68 (2018) 272-285

ABSTRACT

The osteogenic and angiogenic responses of organisms to the ionic products of degradation of bioactive glasses (BGs) are being intensively investigated. The promotion of angiogenesis by copper (Cu) has been known for more than three decades. This element can be incorporated to delivery carriers, such as BGs, and the materials used in biological assays. In this work, Cu-containing mesoporous bioactive glass (MBG) in the SiO2-CaO-P2O5compositional system was prepared incorporating 5% mol Cu (MBG-5Cu) by replacement of the corresponding amount of Ca. The biological effects of the ionic products of MBG biodegradation were evaluated on a well-known endothelial cell line, the bovine aorta endothelial cells (BAEC), as well as in an in vivo zebrafish (Danio rerio) embryo assay. The results suggest that ionic products of both MBG (Cu free) and MBG-5Cu materials promote angiogenesis. In vitro cell cultures show that the ionic dissolution products of these materials are not toxic and promote BAEC viability and migration. In addition, the in vivo assay indicates that both exposition and microinjection of zebrafish embryos with Cu free MBG material increase vessel number and thickness of the subintestinal venous plexus (SIVP), whereas assays using MBG-5Cu enhance this effect.


Marzo, 2018 | DOI: 10.1016/j.actbio.2017.12.032

Robust polarization active nanostructured 1D Bragg Microcavities as optofluidic label-free refractive index sensor


Oliva-Ramirez, M; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 256 (2018) 590-599

ABSTRACT

In this work we report the use of polarization active porous 1D Bragg microcavities (BM) prepared by physical vapor deposition at oblique angles for the optofluidic analysis of liquid solutions. These photonic structures consist of a series of stacked highly porous layers of two materials with different refractive indices and high birefringence. Their operational principle implies filling the pores with the analyzed liquid while monitoring with linearly polarized light the associated changes in optical response as a function of the solution refractive index. The response of both polarization active and inactive BMs as optofluidic sensors for the determination of glucose concentration in water solutions has been systematically compared. Different methods of detection, including monitoring the BM wave retarder behavior, are critically compared for both low and high glucose concentrations. Data are taken in transmission and reflection modes and different options explored to prove the incorporation of these nanostructured transducers into microfluidic systems and/or onto the tip of an optical fiber. This analysis has proven the advantages of the polarization active transducer sensors for the optofluidic analysis of liquids and their robustness even in the presence of light source instabilities or misalignments of the optical system used for detection.


Marzo, 2018 | DOI: 10.1016/j.snb.2017.10.060

Biodegradabiliy of spherical mesoporous silica particles (MCM-41) in simulated body fluid (SBF)


Boccardi, E; Philippart, A; Beltran, AM; Schmidt, J; Liverani, L; Peukert, W; Boccaccini, AR
American Mineralogist, 103 (2018) 350-354

ABSTRACT

Mesoporous silica particles of type MCM-41 (Mobile Composition of Matter No. 41), exhibiting highly ordered mesoporosity (pores with diameter between 2 and 50 nm) and surface roughness, are developed and used as a functional coating on bioactive glass-based scaffolds for bone tissue engineering. The degradability and the mesostructure stability of these novel MCM-41 particles were evaluated. The particles are immersed in simulated body fluid (SBF) for up to 28 days at 37 degrees C, and the variation of the ordered porosity, surface characteristics, and chemical composition of the particles are assessed by SEM-EDX, HRTEM, FTIR, ICP-OES, and pH measurements. The results indicate that the MCM-41 particles are affected by immersion in SBF only during the first few days; however, the surface and the mesopore structure of the particles do not change further with increasing time in SBF. The pore channel diameter increased slightly, confirming the stability of the developed material. The release of dissolved Si-species, which reached a maximum of 260 mg SiO2 per gram of material, could play a key role in gene activation of osteoblast cells and in inducing new bone matrix formation. 


Marzo, 2018 | DOI: 10.2138/am-2018-6281

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires


Filippin, AN; Lopez-Flores, V; Rojas, TC; Saghi, Z; Rico, VJ; Sanchez-Valencia, JR; Espinos, JP; Zitolo, A; Viret, M; Midgley, PA; Barranco, A; Borras, A
Chemistry of Materials, 30 (2018) 879-887

ABSTRACT

In this article we show for the first time the formation of magnetic supported organic nanowires (ONWs) driven by self-assembly of a nonplanar Fe(III) phthalocyanine chloride (FePcCl) molecule. The ONWs grow by a crystallization mechanism on roughness-tailored substrates. The growth methodology consists of a vapor deposition under low vacuum and mild temperature conditions. The structure, microstructure, and chemical composition of the FePcCl NWs are thoroughly elucidated and compared with those of Fe(II) phthalocyanine NWs by a consistent and complementary combination of advanced electron microscopies and X-ray spectroscopies. In a further step, we vertically align the NWs by conformal deposition of a SiO2 shell. Such orientation is critical to analyze the magnetic properties of the FePcCl and FePc supported NWs. A ferromagnetic behavior below 30 K with an easy axis perpendicular to the phthalocyanine plane was observed in the two cases with the FePcCl nanowires presenting a wider hysteresis. These results open the path to the fabrication of nanostructured one-dimensional small-molecule spintronic devices.


Febrero, 2018 | DOI: 10.1021/acs.chemmater.7b04515

In situ monitoring of the phenomenon of electrochemical promotion of catalysis


Espinos, JP; Rico, VJ; Gonzalez-Cobos, J; Sanchez-Valencia, JR; Perez-Dieste, V; Escudero, C; de Lucas-Consuegra, A; Gonzalez-Elipe, AR
Journal of Catalysis, 358 (2018) 27-34

ABSTRACT

In this work we investigate by in-situ near-ambient pressure photoemission (NAPP) spectroscopy the phenomenon of Electrochemical Promotion of Catalysis (EPOC). We studied the reduction and diffusion kinetics of alkaline ions in a solid electrolyte cell formed by a nickel electrode supported on K+-beta-alumina electrolyte. Experiments in ultra-high vacuum and in the presence of steam showed that the amount of potassium atoms supplied to the surface is probably affected by nickel electronic modifications induced by adsorbed OH- groups. It was also deduced that part of the segregated potassium would be adsorbed at inner interfaces where it would be inaccessible to the photoelectron analyzer. A migration mechanism of the promoter is proposed consisting in: (i) the electrochemical reduction of the alkali ions (potassium) at the Ni/solid electrolyte/gas interface; (ii) the spillover of potassium atoms onto the Ni gas-exposed surface; and (iii) the diffusion of potassium atoms to Ni inner grain boundary interfaces.


Febrero, 2018 | DOI: 10.1016/j.jcat.2017.11.027

Microstructural engineering and use of efficient poison resistant Au-doped Ni-GDC ultrathin anodes in methane-fed solid oxide fuel cells


Garcia-Garcia, FJ; Yubero, F; Gonzalez-Elipe, AR; Lambert, RM
International Journal of Refractory Metals & Hard Materials, 43 (2018) 885-893

ABSTRACT

Ultrathin porous solid oxide fuel cell (SOFC) anodes consisting of nickel-gadolinia-dopedceria (Ni-GDC) cermets with a unique porous micro-columnar architecture with intimate contact between the GDC and the Ni phases were made by magnetron sputtering at an oblique deposition angle and characterised in detail by a variety of methods prior to use in hydrogen or methane-fuelled SOFCs. These Ni-GDC anodes exhibited excellent transport properties, were robust under thermal cycling and resistant to delamination from the underlying yttria-stabilised zirconia electrolyte. Similarly prepared Au-doped Ni-GDC anodes exhibited the same morphology, porosity and durability. The gold associated exclusively with the Ni component in which it was present as a surface alloy. Strikingly, whatever their treatment, a substantial amount of Ce3+ persisted in the anodes, even after operation at 800 degrees C under fuel cell conditions. With hydrogen as fuel, the un-doped and Au doped Ni-GDC anodes exhibited identical electrochemical performances, comparable to that of much thicker commercial state-of-the-art Ni-GDC anodes. However, under steam reforming conditions with CH4/H(2)0 mixtures the behaviour of the Au-doped Ni-GDC anodes were far superior, exhibiting retention of good power density and dramatically improved resistance to deactivation by carbon deposition. Thus two distinct beneficial effects contributed to overall performance: persistence of Ce3+ in the working anodes could induce a strong metal-support interaction with Ni that enhanced the catalytic oxidation of methane, while formation of a Ni Au surface alloy that inhibited carbonisation and poisoning of the active nickel surface. 


Enero, 2018 | DOI: 10.1016/j.ijhydene.2017.11.020

Nanostructured hybrid device mimicking bone extracellular matrix as local and sustained antibiotic delivery system


Borrego-Gonzalez, S; Romero-Sanchez, LB; Blazquez, J; Diaz-Cuenca, A
Microporous and Mesoporous Materials, 256 (2018) 165-176

ABSTRACT

A fluidic permeable and stable in wet media, MBG-NfGel, device consisting of a mesoporous ceramic embodied in a nanofibrillar biodegradable polymer has been processed using appropriate thermally induced phase separation (TIPS) processing variables of 5.4% (wt/v) gelatin in 50/50 water/ethanol (v/v) ratio. The device comprises high surface area mesoporous bioactive glass (MBG) microparticles within a fibrous matrix of 170 nm average diameter nanofibers gelatin, forming a meshwork of 0.2-1.6 mu m range voids. Gentamicin sulphate (GS) antibiotic high loading capacity and sustained release ability, as well as in vitro bioactivity and osteoprogenitor cells biocompatibility supports long-term antibacterial and bone growth stimulation properties. Antibiotic local delivery functionality in vitro of this device has been analysed and discussed in relation to other systems previously reported. The presented device properties as well as its industrial scalability potential, in terms of process reliability and absence of toxic chemical agents, low raw material biopolymer cost and immunogenicity, are other important advantages. These advantages rank MBG-NfGel device as a potential candidate to further development for application as local antibiotic device in bone surgery and therapy.


Enero, 2018 | DOI: 10.1016/j.micromeso.2017.08.010

Nickel/Copper Bilayer-modified Screen Printed Electrode for Glucose Determination in Flow Injection Analysis


Salazar, P.; Rico, V.; Gonzalez-Elipe, Agustin R.
Electroanalysis, 30 (2018) 187-193

ABSTRACT

This work reports about the performance of a Ni/Cu-modified screen printed electrodes (SPE/Ni/Cu), prepared by physical vapor deposition (PVD) in an oblique angle configuration (OAD), for non-enzymatic glucose sensing applications. SPE/Ni/Cu electrodes showed an excellent reversibility and a catalytic behavior for detection of glucose that were controlled by the diffusion of reactants up to the active sites at the electrode surface. The study with a flow injection analysis (FIA) setup of the main experimental variables affecting the detection process has shown that the developed electrode system had an excellent glucose sensitivity of 1.04AM(-1)cm(-2) (R-2:0.999), a linear response up to 1mM, a limit of detection of 0.33M and a time of analysis of ca. 30s per sample. The selectivity of the sensor was checked against various interferences, including ascorbic acid, uric acid, acetaminophen and other sugars, in all cases with excellent results. The feasibility of using this sensor for practical applications was successfully confirmed by determining the glucose concentration in different commercial beverages.


Enero, 2018 | DOI: 10.1002/elan.201700592



2017


Silver and gold nanoparticles in nanometric confined templates: synthesis and alloying within the anisotropic pores of oblique angle deposited films


Parra-Barranco, J., Sánchez-Valencia, J.R., Barranco, A., González-Elipe, A.R.
Nanotechnology, 28 (2017) 485602

ABSTRACT

In this work we have developed an infiltration methodology to incorporate metal nanoparticles (NPs) of controlled size and shape into the open voids available in oblique angle deposited thin films. These NPs exhibited well-defined surface plasmon resonances (SPRs). The nanometric confined space provided by their porous microstructure has been used as a template for the growth of anisotropic NPs with interesting SPR properties. The fabrication methodology has been applied for the preparation of films with embedded Ag and Au NPs with two associated plasmon resonance features that developed a dichroic behaviour when examined with linearly polarized light. A confined alloying process was induced by near IR nanosecond laser irradiation yielding bimetallic NPs with SPR features covering a large zone of the electromagnetic spectrum. The possibilities of the method for the tailored fabrication of a wide range colour palette based on SPR features are highlighted.


Diciembre, 2017 | DOI: 10.1088/1361-6528/aa92af

Micron-scale wedge thin films prepared by plasma enhanced chemical vapor deposition


Lopez-Santos, MC; Alvarez, R; Palmero, A; Borras, A; del Campo, RC; Holgado, M; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 14 (2017) e1700043

ABSTRACT

Wedge-shaped materials are currently employed for optical analyses and sensing applications. In this paper, we present an easy to implement plasma enhanced chemical vapor deposition procedure to grow wedge-shaped thin films with controlled slope at the scale of few hundred microns. The method relies on the use of few tenths micron height obstacles to alter the laminar flow of precursor gas during deposition and is applied for the fabrication of wedge-shaped ZnO thin films. Local interference patterns, refractive index, and birefringence of the films have been measured with one micron resolution using a specially designed optical set-up. Their micro- and nano-structures have been characterized by means of scanning electron microscopy and theoretically reproduced by Monte Carlo calculations.


Diciembre, 2017 | DOI: 10.1002/ppap.201700043

Determination of the thickness of the embedding phase in 0D nanocomposites


Martinez-Martinez, D; Sanchez-Lopez, JC
Applied Surface Science, 421 (2017) 179-184

ABSTRACT

0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting systems which may show properties that are beyond those observed in the original constituents alone. One of the main parameters to understand the behavior of such nanocomposites is the determination of the separation between two adjacent nanoparticles, in other words, the thickness of the embedding phase. However, its experimental measurement is extremely complicated. Therefore, its evaluation is performed by an indirect approach using geometrical models. The ones typically used represent the nanoparticles by cubes or spheres. 
In this paper the used geometrical models are revised, and additional geometrical models based in other parallelohedra (hexagonal prism, rhombic and elongated dodecahedron and truncated octahedron) are presented. Additionally, a hybrid model that shows a transition between the spherical and tessellated models is proposed. Finally, the different approaches are tested on a set of titanium carbide/amorphous carbon (TiC/a-C) nanocomposite films to estimate the thickness of the a-C phase and explain the observed hardness properties. 


Noviembre, 2017 | DOI: 10.1016/j.apsusc.2016.12.081

Structural control in porous/compact multilayer systems grown by magnetron sputtering


Garcia-Valenzuela, A; Lopez-Santos, C; Alvarez, R; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 28 (2017) 46

ABSTRACT

In this work we analyze a phenomenon that takes place when growing magnetron sputtered porous/compact multilayer systems by alternating the oblique angle and the classical configuration geometries. We show that the compact layers develop numerous fissures rooted in the porous structures of the film below, in a phenomenon that amplifies when increasing the number of stacked layers. We demonstrate that these fissures emerge during growth due to the high roughness of the porous layers and the coarsening of a discontinuous interfacial region. To minimize this phenomenon, we have grown thin interlayers between porous and compact films under the impingement of energetic plasma ions, responsible for smoothing out the interfaces and inhibiting the formation of structural fissures. This method has been tested in practical situations for compact TiO2/porous SiO2 multilayer systems, although it can be extrapolated to other materials and conditions.


Noviembre, 2017 | DOI: 10.1088/1361-6528/aa8cf4

Towards Extending Solar Cell Lifetimes: Addition of a Fluorous Cation to Triple Cation-Based Perovskite Films


Salado, M; Fernandez, MA; Holgado, JP; Kazim, S; Nazeeruddin, MK; Dyson, PJ; Ahmad, S
Chemsuschem, 10 (2017) 3846-3853

ABSTRACT

Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs-0.05(MA(0.15)FA(0.85))(0.95)Pb(I0.85Br0.15)(3) (MA= methylammonium; FA= formamidinium) has been shown to influence its stability. The resulting materials, which vary according to the amount of the fluorous-functionalized imidazolium cation present during fabrication, display a prolonged tolerance to atmospheric humidity (> 100 days) along with power conversion efficiencies exceeding 16%. This work provides a general route that can be implemented in a variety of perovskites and highlights a promising way to increase perovskite solar cell stability.


Octubre, 2017 | DOI: 10.1002/cssc.201700797

HoF3 and DyF3 Nanoparticles as Contrast Agents for High-Field Magnetic Resonance Imaging


Gonzalez-Mancebo, Daniel; Becerro, Ana I.; Rojas, T. Cristina; Garcia-Martin, Maria L.; de la Fuente, Jesus M.; Ocana, Manuel
Particle & particle systems characterization, 34 (2017) art. 1700116

ABSTRACT

Clinical contrast agents (CAs) currently used in magnetic resonance imaging (MRI) at low fields are less effective at high magnetic fields. The development of new CAs is mandatory to improve diagnostic capabilities of the new generation of high field MRI scanners. The purpose of this study is to synthesize uniform, water dispersible LnF3 (Ln = Ho, Dy) nanoparticles (NPs) and to evaluate their relaxivity at high magnetic field (9.4 T) as a function of size and composition. Two different types of HoF3 NPs are obtained by homogeneous precipitation in ethylene glycol at 120 °C. The use of holmium acetate as holmium precursor leads to rhombus-like nanoparticles, while smaller, ellipsoid-like nanoparticles are obtained when nitrate is used as the holmium salt. To explain this behavior, the mechanism of formation of both kinds of particles is analyzed in detail. Likewise, rhombus-like DyF3 nanoparticles are prepared following the same method as for the rhombus-like HoF3 nanoparticles. We have found, to the best of knowledge, the highest transverse relaxivity values at 9.4 T described in the literature for this kind of CAs. Finally, the LnF3 NPs have shown negligible cytotoxicity for C6 rat glioma cells for concentrations up to 0.1 mg mL−1.


Octubre, 2017 | DOI: 10.1002/ppsc.201700116

Incorporation of Calcium Containing Mesoporous (MCM-41-Type) Particles in Electrospun PCL Fibers by Using Benign Solvents


Liverani, L.;Boccardi, E.; Beltrán, A.M.; Boccaccini, A.R.
Polymers, 9 (2017) 487

ABSTRACT

The electrospinning technique is a versatile method for the production of fibrous scaffolds able to resemble the morphology of the native extra cellular matrix. In the present paper, electrospinning is used to fabricate novel SiO2particles (type MCM-41) containing poly(epsilon-caprolactone) (PCL) fibers. The main aims of the present work are both the optimization of the particle synthesis and the fabrication of composite fibers, obtained using benign solvents, suitable as drug delivery systems and scaffolds for soft tissue engineering applications. The optimized synthesis and characterization of calcium-containing MCM-41 particles are reported. Homogeneous bead-free composite electrospun mats were obtained by using acetic acid and formic acid as solvents; neat PCL electrospun mats were used as control. Initially, an optimization of the electrospinning environmental parameters, like relative humidity, was performed. The obtained composite nanofibers were characterized from the morphological, chemical and mechanical points of view, the acellular bioactivity of the composite nanofibers was also investigated. Positive results were obtained in terms of mesoporous particle incorporation in the fibers and no significant differences in terms of average fiber diameter were detected between the neat and composite electrospun fibers. Even if the Ca-containing MCM-41 particles are bioactive, this property is not preserved in the composite fibers. In fact, during the bioactivity assessment, the particles were released confirming the potential application of the composite fibers as a drug delivery system. Preliminary in vitro tests with bone marrow stromal cells were performed to investigate cell adhesion on the fabricated composite mats, the positive obtained results confirmed the suitability of the composite fibers as scaffolds for soft tissue engineering.


Octubre, 2017 | DOI: 10.3390/polym9100487

Vapor and liquid optical monitoring with sculptured Bragg microcavities


Oliva-Ramirez, M; Gil-Rostra, J; Lopez-Santos, MC; Gonzalez-Elipe, AR; Yubero, F
Journal of Nanophotonics, 11 (2017) 046009

ABSTRACT

Sculptured porous Bragg microcavities (BMs) formed by the successive stacking of columnar SiO2 and TiO2 thin films with a zig-zag columnar microstructure are prepared by glancing angle deposition. These BMs act as wavelength-dependent optical retarders. This optical behavior is attributed to a self-structuration of the stacked layers involving the lateral association of nanocolumns in the direction perpendicular to the main flux of particles during the multilayer film growth, as observed by focused ion beam scanning electron microscopy. The retardance of these optically active BMs can be modulated by dynamic infiltration of their open porosity with vapors, liquids, or solutions with different refractive indices. The tunable birefringence of these nanostructured photonic systems has been successfully simulated with a simple model that assumes that each layer within the BMs stack has uniaxial birefringence. The sculptured BMs have been incorporated as microfluidic chips for optical transduction for label-free vapor and liquid sensing. Several examples of the detection performance of these chips, working either in reflection or transmission configuration, for the optical monitoring of vapor and liquids of different refractive indices and aqueous solutions of glucose flowing through the microfluidic chips are described.


Octubre, 2017 | DOI: 10.1117/1.JNP.11.046009

High performance novel gadolinium doped ceria/yttria stabilized zirconia/nickel layered and hybrid thin film anodes for application in solid oxide fuel cells


Garcia-Garcia, FJ; Beltran, AM; Yubero, E; Gonzalez-Elipe, AR; Lambert, RM
Journal of Power Sources, 363 (2017) 251-259

ABSTRACT

Magnetron sputtering under oblique angle deposition was used to produce Ni-containing ultra thin film anodes comprising alternating layers of,gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) of either 200 nm or 1000 nm thickness. The evolution of film structure from initial deposition, through calcination and final reduction was examined by XRD, SEM, TEM and TOF-SIMS. After subsequent fuel cell usage, the porous columnar architecture of the two-component layered thin film anodes was maintained and their resistance to delamination from the underlying YSZ electrolyte was superior to that of corresponding single component Ni-YSZ and Ni-GDC thin films. Moreover, the fuel cell performance of the 200 nm layered anodes compared favorably with conventional commercially available thick anodes. The observed dependence of fuel cell performance on individual layer thicknesses prompted study of equivalent but more easily fabricated hybrid anodes consisting of simultaneously deposited Ni-GDC and Ni-YSZ, which procedure resulted in exceptionally intimate mixing and interaction of the components. The hybrids exhibited very unusual and favorable I-V characteristics, along with exceptionally high power densities at high currents. Their discovery is the principal contribution of the present work. 


Septiembre, 2017 | DOI: 10.1016/j.jpowsour.2017.07.085

Enhanced green fluorescent protein in optofluidic Fabry-Perot microcavity to detect laser induced temperature changes in a bacterial culture


Lahoz, F; Martin, IR; Walo, D; Freire, R; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Applied Physics Letters, 111 (2017) 111103

ABSTRACT

Thermal therapy using laser sources can be used in combination with other cancer therapies to eliminate tumors. However, high precision temperature control is required to avoid damage in healthy surrounding tissues. Therefore, in order to detect laser induced temperature changes, we have used the fluorescence signal of the enhanced Green Fluorescent Protein (eGFP) over-expressed in an E. coli bacterial culture. For that purpose, the bacteria expressing eGFP are injected in a Fabry-Perot (FP) optofluidic planar microcavity. In order to locally heat the bacterial culture, external infrared or ultraviolet lasers were used. Shifts in the wavelengths of the resonant FP modes are used to determine the temperature increase as a function of the heating laser pump power. Laser induced local temperature increments up to 6-7 degrees C were measured. These results show a relatively easy way to measure laser induced local temperature changes using a FP microcavity and using eGFP as a molecular probe instead of external nanoparticles, which could damage/alter the cell. Therefore, we believe that this approach can be of interest for the study of thermal effects in laser induced thermal therapies. 


Septiembre, 2017 | DOI: 10.1063/1.4990870

In Vitro and in Vivo Study of Poly(Lactic-co-Glycolic) (PLGA) Membranes Treated with Oxygen Plasma and Coated with Nanostructured Hydroxyapatite Ultrathin Films for Guided Bone Regeneration Processes


Torres-Lagares, D; Castellanos-Cosano, L; Serrera-Figallo, MA; Garcia-Garcia, FJ; Lopez-Santos, C; Barranco, A; Elipe, ARG; Rivera-Jimenez, C; Gutierrez-Perez, JL
Polymers, 9 (2017) art. 410

ABSTRACT

The novelty of this study is the addition of an ultrathin layer of nanostructured hydroxyapatite (HA) on oxygen plasmamodified poly(lactic-co-glycolic) (PLGA) membranes (PO2) in order to evaluate the efficiency of this novel material in bone regeneration. Methods: Two groups of regenerative membranes were prepared: PLGA (control) and PLGA/PO2/HA (experimental). These membranes were subjected to cell cultures and then used to cover bone defects prepared on the skulls of eight experimental rabbits. Results: Cell morphology and adhesion of the osteoblasts to the membranes showed that the osteoblasts bound to PLGA were smaller and with a lower number of adhered cells than the osteoblasts bound to the PLGA/PO2/HA membrane (p < 0.05). The PLGA/PO2/HA membrane had a higher percentage of viable cells bound than the control membrane (p < 0.05). Both micro-CT and histological evaluation confirmed that PLGA/PO2/HA membranes enhance bone regeneration. A statistically significant difference in the percentage of osteoid area in relation to the total area between both groups was found. Conclusions: The incorporation of nanometric layers of nanostructured HA into PLGA membranes modified with PO2 might be considered for the regeneration of bone defects. PLGA/PO2/HA membranes promote higher osteosynthetic activity, new bone formation, and mineralisation than the PLGA control group.


Septiembre, 2017 | DOI: 10.3390/polym9090410

The role of cobalt hydroxide in deactivation of thin film Co-based catalysts for sodium borohydride hydrolysis


Paladini, M; Arzac, GM; Godinho, V; Hufschmidt, D; de Haro, MCJ; Beltran, AM; Fernandez, A
Applied Catalysis B-Environmental, 210 (2017) 342-351

ABSTRACT

Deactivation of a Co catalyst prepared as thin film by magnetron sputtering was studied for the sodium borohydride (SB) hydrolysis reaction under different conditions. Under high SB concentration in single run experiments, the formation of a B-O passivating layer was observed after 1.5 and 24 h use. This layer was not responsible for the catalyst deactivation. Instead, a peeling-off mechanism produced the loss of cobalt. This peeling-off mechanism was further studied in cycling experiments (14 cycles) under low SB concentrations. Ex-situ study of catalyst surface after use and solid reaction products (precipitates) was performed by X-Ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The presence of cobalt hydroxide and oxyhydroxide was detected as major components on the catalyst surface after use and as precipitates in the supernatant solutions after washing. Cobalt borate, cobalt carbonate and oxycarbonate were also formed but in lesser amounts. These oxidized cobalt species were formed and further detached from the catalyst at the end of the reaction and/or during catalyst washing by decomposition of the unstable in-situ formed cobalt boride. Leaching of cobalt soluble species was negligible. Thin film mechanical detachment was also found but in a smaller extent. To study the influence of catalyst composition on deactivation processes, cycling experiments were performed with Co-B and Co-C catalysts, also prepared as thin films. We found that the deactivation mechanism proposed by us for the pure Co catalyst also occurred for a different pure Co (prepared at higher pressure) and the Co-B and Co-C samples in our experimental conditions. 


Agosto, 2017 | DOI: 10.1016/j.apcatb.2017.04.005

One-reactor plasma assisted fabrication of ZnO@TiO2 multishell nanotubes: assessing the impact of a full coverage on the photovoltaic performance


Filippin, Alejandro Nicolas; Macias-Montero, Manuel; Saghi, Zineb; Idigoras, Jesus; Burdet, Pierre; Sanchez-Valencia, Juan R.; Barranco, Angel; Migdley, Paul A.; Anta, Juan A.; Borras, Ana
Scientific Reports, 7 (2017) art 9621

ABSTRACT

This paper addresses the fabrication of vertically aligned ZnO@TiO2multishell nanotubes by a combined full vacuum-plasma approach at mild temperatures. The growth is carried out within the premises of a one-reactor approach, i.e. minimizing the number of vacuum chambers and sample transferences. In this way, the interface between ZnO and TiO2 is fully preserved from humidity thus increasing ZnO durability and stability. These nanostructures are studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy in STEM (EDX-STEM). High density one-dimensional arrays of these nanotubes formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The evolution of the dye adsorption capacity and solar cells parameters are explored as a function of the crystallinity and thickness of the TiO2 shell. The results show the critical effect of a full coverage by TiO2 of ZnO core to explain the mixed results found in the literature.


Agosto, 2017 | DOI: 10.1038/s41598-017-09601-7

Optical properties and electronic transitions of zinc oxide, ferric oxide, cerium oxide, and samarium oxide in the ultraviolet and extreme ultraviolet


Pauly, N; Yubero, F; Espinos, JP; Tougaard, S
Applied Optics, 56 (2017) 6611-6621

ABSTRACT

Optical properties and electronic transitions of four oxides, namely zinc oxide, ferric oxide, cerium oxide, and samarium oxide, are determined in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy using primary electron energies in the range 0.3 - 2.0 keV. This technique allows the evaluation of the optical response in these ultraviolet spectral regions of a thin layer of material, and the analysis is straightforward. It is performed within the dielectric response theory by means of the QUEELS-epsilon(k,omega)-REELS software developed by Tougaard and Yubero [Surf. Interface Anal. 36, 824 ( 2004)]. The method consists basically in the fitting of experimentally determined single-scattering electron energy loss cross sections with a parametric energy loss function of the corresponding material, to the one calculated within a dielectric response formalism. The obtained refractive index and extinction coefficients, as well as the identified electronic transitions are compared, when available, with previously published results. 


Agosto, 2017 | DOI: 10.1364/AO.56.006611

Plasma assisted deposition of single and multistacked TiO2 hierarchical nanotube photoanodes


Filippin, AN; Sanchez-Valencia, JR; Idigoras, J; Rojas, TC; Barranco, A; Anta, JA; Borras, A
Nanoscale, 9 (2017) 8133-8141

ABSTRACT

We present herein an evolved methodology for the growth of nanocrystalline hierarchical nanotubes combining physical vapor deposition of organic nanowires (ONWs) and plasma enhanced chemical vacuum deposition of anatase TiO2 layers. The ONWs act as vacuum removable 1D and 3D templates, with the whole process occurring at temperatures ranging from RT to 250 degrees C. As a result, a high density of hierarchical nanotubes with tunable diameter, length and tailored wall microstructures are formed on a variety of processable substrates as metal and metal oxide films or nanoparticles including transparent conductive oxides. The reiteration of the process leads to the development of an unprecedented 3D nanoarchitecture formed by stacking the layers of hierarchical TiO2 nanotubes. As a proof of concept, we present the superior performance of the 3D nanoarchitecture as a photoanode within an excitonic solar cell with efficiencies as high as 4.69% for a nominal thickness of the anatase layer below 2.75 mu m. Mechanical stability and straightforward implementation in devices are demonstrated at the same time. The process is extendable to other functional oxides fabricated by plasma-assisted methods with readily available applications in energy harvesting and storage, catalysis and nanosensing.


Julio, 2017 | DOI: 10.1039/c7nr00923b

Low-Temperature Plasma Processing of Platinum Porphyrins for the Development of Metal Nanostructured Layers


Filippin, AN; Sanchez-Valencia, JR; Idigoras, J; Macias-Montero, M; Alcaire, M; Aparicio, FJ; Espinos, JP; Lopez-Santos, C; Frutos, F; Barranco, A; Anta, JA; Borras, A
Advanced Materials Interfaces, 4 (2017) 1601233

ABSTRACT

This article establishes the bases for a vacuum and plasma supported methodology for the fabrication at mild temperatures of nanostructured platinum in the form of porous layers and nanocolumns using platinum octaethylporphyrin as precursor. In addition, the application of these materials as tunable optical filters and nano-counterelectrodes is proved. On one hand, the transparency in the ultraviolet-visible-near infrared range can be adjusted precisely between 70% and 1% by tuning the deposition and processing conditions, obtaining a high spectral planarity. Deviations of the spectra from an ideal flat filter are below 4%, paving the way to the fabrication of neutral density filters. The transparency limit values yield a sheet resistivity of approximate to 1350 and 120 Omega square(-1), respectively. On the other hand, the catalytic properties of the nanostructures are further demonstrated by their implementation as counterelectrodes of excitonic solar cells surpassing the performance of commercial platinum as counterelectrode in a 20% of the overall cell efficiency due to simultaneous enhancement of short-circuit photocurrent and open-circuit photovoltage. One of the most interesting features of the developed methodology is its straightforward application to other metal porphyrins and phthalocyanines readily sublimable under mild vacuum and temperature conditions.


Julio, 2017 | DOI: 10.1002/admi.201601233

Formation of Subsurface W5+ Species in Gasochromic Pt/WO3 Thin Films Exposed to Hydrogen


Castillero, Pedro; Rico-Gavira, Victor; Lopez-Santos, Carmen; Barranco, Angel; Perez-Dieste, Virginia; Escudero, Carlos; Espinos, Juan P.; Gonzalez-Elipe, Agustin R.
Journal of Physical Chemistry C, 121 (2017) 15719-15727

ABSTRACT

M/WO3 (M = Pt, Pd) systems formed by a porous WO3 thin film decorated by metal nanoparticles are known for their reversible coloring upon exposure to H2 at room temperature. In this work, this gasochromic behavior is investigated in situ by means of near-ambient photoemission (NAPP). Pt/WO3 systems formed by very small Pt nanoparticles (10 ± 1 nm average size) incorporated in the pores of nanocolumnar WO3 thin films prepared by magnetron sputtering at an oblique angle have been exposed to a small pressure of hydrogen at ambient temperature. The recorded UV–vis transmission spectra showed the reversible appearance of a very intense absorption band responsible for the blue coloration of these gasochromic films. In an equivalent experiment carried out in the NAPP spectrometer, W 4f, O 1s, Pt 4f, and valence band photoemission spectra have been recorded at various photon energies to follow the evolution of the reduced tungsten species and hydroxyl groups formed upon film exposure to hydrogen. The obtained results are compared with those of a conventional X-ray photoemission study after hydrogen exposure between 298 and 573 K. As investigated by NAPP, the gasochromic behavior at 298 K is accounted for by a reaction scheme in which hydrogen atoms resulting from the dissociation of H2 onto the Pt nanoparticles are spilt over to the WO3 substrate where they form surface OH–/H2O species and subsurface W5+ cations preferentially located in buried layers of the oxide network.


Julio, 2017 | DOI: 10.1021/acs.jpcc.7b03385

Surface chemistry and germination improvement of Quinoa seeds subjected to plasma activation


Gomez-Ramierez, A.; Lopez-Santos, C.; Cantos, M.; Garcia, J. L.; Molina, R.; Cotrino, J.; Espinos, J. P.; Gonzalez-Elipe, A. R.
Scientific Reports, 7 (2017) art. 5924

ABSTRACT

Plasma treatment is recognized as a suitable technology to improve germination efficiency of numerous seeds. In this work Quinoa seeds have been subjected to air plasma treatments both at atmospheric and low pressure and improvements found in germination rate and percentage of success. Seed water uptake by exposure to water vapor, although slightly greater for plasma treated seeds, did not justify the observed germination improvement. To identify other possible factors contributing to germination, the chemical changes experienced by outer parts of the seed upon plasma exposure have been investigated by X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM-EDX). XPS revealed that the outer layers of the Quinoa plasma treated seeds were highly oxidized and appeared enriched in potassium ions and adsorbed nitrate species. Simultaneously, SEM-EDX showed that the enrichment in potassium and other mineral elements extended to the seed pericarp and closer zones. The disappearance from the surface of both potassium ions and nitrate species upon exposure of the plasma treated seeds to water vapor is proposed as a factor favoring germination. The use of XPS to study chemical changes at seed surfaces induced by plasma treatments is deemed very important to unravel the mechanisms contributing to germination improvement.


Julio, 2017 | DOI: 10.1038/s41598-017-06164-5

Impact of moisture on efficiency-determining electronic processes in perovskite solar cells


Salado, Manuel; Contreras-Bernal, Lidia; Calio, Laura; Todinova, Anna; Lopez-Santos, Carmen; Ahmad, Shahzada; Borras, Ana; Idigoras, Jesus; Anta, Juan A.
Journal of Materials Chemistry A, 5 (2017) 10917-10927

ABSTRACT

Moisture-induced degradation in perovskite solar cells was thoroughly investigated by structural (SEM, EDS, XRD and XPS) and device characterization (impedance and intensity modulated photocurrent spectroscopy) techniques. Both the influence of the perovskite composition and the nature of the hole selective material were analyzed. The degradation rate was found to be significantly slower for mixed perovskites and P3HT-based devices. However, for a fixed degradation degree (defined as a 50% drop from the initial photocurrent), all configurations show similar features in small-perturbation analysis. Thus, a new mid-frequency signal appears in the impedance response, which seems to be related to charge accumulation at the interfaces. In addition, faster recombination, with a more important surface contribution, and slower transport were clearly inferred from our results. Both features can be associated with the deterioration of the contacts and the formation of a higher number of grain boundaries.


Junio, 2017 | DOI: 10.1039/c7ta02264f

In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes


Macias-Montero, Manuel; Lopez-Santos, Carmen; Nicolas Filippin, A.; Rico, Victor J.; Espinos, Juan P.; Fraxedas, Jordi; Perez-Dieste, Virginia; Escudero, Carlos; Gonzalez-Elipe, Agustin R.; Borras, Ana
Langmuir, 33 (2017) 6449-6456

ABSTRACT

One-dimensional (1D) nanostructured surfaces based on high-density arrays of nanowires and nanotubes of photoactive titanium dioxide (TiO2) present a tunable wetting behavior from superhydrophobic to superhydrophilic states. These situations are depicted in a reversible way by simply irradiating with ultraviolet light (superhydrophobic to superhydrophilic) and storage in dark. In this article, we combine in situ environmental scanning electron microscopy (ESEM) and near ambient pressure photoemission analysis (NAPP) to understand this transition. These experiments reveal complementary information at microscopic and atomic level reflecting the surface wettability and chemical state modifications experienced by these 1D surfaces upon irradiation. We pay special attention to the role of the water condensation mechanisms and try to elucidate the relationship between apparent water contact angles of sessile drops under ambient conditions at the macroscale with the formation of droplets by water condensation at low temperature and increasing humidity on the nanotubes surfaces. Thus, for the as-grown nanotubes, we reveal a metastable and superhydrophobic Cassie state for sessile drops that tunes toward water dropwise condensation at the microscale compatible with a partial hydrophobic Wenzel state. For the UV-irradiated surfaces, a filmwise wetting behavior is observed for both condensed water and sessile droplets. NAPP analyses show a hydroxyl accumulation on the as-grown nanotubes surfaces during the exposure to water condensation conditions, whereas the water filmwise condensation on a previously hydroxyl enriched surface is proved for the superhydrophilic counterpart.


Junio, 2017 | DOI: 10.1021/acs.langmuir.7b00156

About the enhancement of chemical yield during the atmospheric plasma synthesis of ammonia in a ferroelectric packed bed reactor


Gomez-Ramirez, Ana; Montoro-Damas, Antonio M.; Cotrino, Jose; Lambert, Richard M.; Gonzalez-Elipe, Agustin R.
Plasma Processes and Polymers, 14 (2017) e1600081

ABSTRACT

Plasma reactions offer an attractive alternative route for the synthesis of a variety of valuable chemical compounds. Here we investigate the parameters that determine the efficiency of ammonia synthesis in a ferroelectric packed bed dielectric barrier discharge (DBD) reactor. The effects of varying the operating frequency, the size of the ferroelectric pellets and the inter-electrode distance have been systematically studied. Under optimised conditions nitrogen conversions in excess of 7% were achieved, higher than those previously obtained using DBD reactors. These findings are discussed with respect to variations in the electrical characteristics of the reactor under operating conditions and in the light of emission spectra obtained as a function of reactant flow rates. These encouraging results signpost future developments that could very substantially improve the efficiency of ammonia synthesis by means of DBD technology.


Junio, 2017 | DOI: 10.1002/ppap.201600081

A compact and portable optofluidic device for detection of liquid properties and label-free sensing


Lahoz, F; Martin, IR; Walo, D; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Journal of Physics D: Applied Physics, 50 (2017) 21

ABSTRACT

Optofluidic lasers have been widely investigated over the last few years mainly because they can be easily integrated in sensor devices. However, high power pulse lasers arc required as excitation sources, which, in practice, limit the portability of the system. Trying to overcome some of these limitations, in this paper we propose the combined use of a small CW laser with a Fabry-Perot optofluidic planar microcavity showing high sensitivity and versatility for detection of liquid properties and label-free sensing. Firstly, a fluorescein solution in ethanol is used to demonstrate the high performances of the FP microcavity as a temperature sensor both in the laser (high pump power above laser threshold) and in the fluorescence (low pump power) regimes. A shift in the wavelength of the resonant cavity modes is used to detect changes in the temperature and our results show that high sensitivities could be already obtained using cheap and portable CW diode lasers. In the second part of the paper, the demonstration of this portable device for label-free sensing is illustrated under low CW pumping. The wavelength positions of the optolluidic resonant modes are used to detect glucose concentrations in water solutions using a protein labelled with a fluorescent dye as the active medium.


Junio, 2017 | DOI: 10.1088/1361-6463/aa6cdd

High surface area biopolymeric-ceramic scaffolds for hard tissue engineering


Romero-Sanchez, LB; Borrego-Gonzalez, S; Diaz-Cuenca, A
Biomedical Physics & Engineering Express, 3 (2017) art UNSP 035012

ABSTRACT

The development of scaffolds mimicking native bone tissue composition and structure is a challenge in bone tissue engineering. 3D scaffolds with both an interconnected macropore structure and nanotextured surfaces are required. However, 3D scaffolds processed by microfabrication usually lack of nanotextured surface, while nanotextured materials generated by bottom-up nanofabrication are difficult to process conforming scaffolds having well interconnected microsized cavities. In this work, the processing of reticulated (macropore interconnected) structures using nanostructured precursors has been performed to improve the mechanical properties of the scaffolds. The application of a fibrillar collagen coating, using less than 1 wt% collagen per scaffold, has allow a significant increase of the compressive strength while preserving a high surface area and nanopore accessibility. Besides, the fibrillar nanostructured collagen coating promotes hydroxyapatite mineralization. Two different collagen-coating procedures are applied showing interesting differences in terms of mechanical performance.


Junio, 2017 | DOI: 10.1088/2057-1976/aa7001

1-dimensional TiO2 nano-forests as photoanodes for efficient and stable perovskite solar cells fabrication


Salado, M; Oliva-Ramirez, M; Kazim, S; Gonzalez-Elipe, AR; Ahmad, S
Nano Energy, 35 (2017) 215-222

ABSTRACT

During the last years, perovskite solar cells have gained increasing interest among the photovoltaic community, in particularly after reaching performances at par with mature thin film based PV. This rapid evolution has been fostered by the compositional engineering of perovskite and new device architectures. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional vertically oriented TiO2 nano-forests. These vertically oriented porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration, a method which is scalable to fabricate large area devices. Mixed (MA0.15FA0.85)Pb(I0.85Br0.15)3 or triple cation Cs0.05(MA0.15FA0.85)0.95Pb(I0.85Br0.15)3 based perovskites were then infiltrated into these 1-dimensional nanostructures and power conversion efficiencies of 16.8% along with improved stability was obtained. The devices fabricated using 1D-TiO2 were found to be more stable compare to the classical 3-dimensional TiO2 photoanodes prepared by wet chemistry. These 1-D photoanodes will be of interest for scaling up the technology and in other opto-electrical devices as they can be easily fabricated utilizing industrially adapted methodologies.


Mayo, 2017 | DOI: 10.1016/j.nanoen.2017.03.034

Critical Role of Oxygen in Silver-Catalyzed Glaser-Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles


Orozco, N; Kyriakou, G; Beaumont, SK; Sanz, JF; Holgado, JP; Taylor, MJ; Espinos, JP; Marquez, AM; Watson, DJ; Gonzalez-Elipe, AR; Lambert, RM
ACS Catalysis, 7 (2017) 3113-3120

ABSTRACT

The essential role of oxygen in enabling heterogeneously catalyzed Glaser–Hay coupling of phenylacetylene on Ag(100) was elucidated by STM, laboratory and synchrotron photoemission, and DFT calculations. In the absence of coadsorbed oxygen, phenylacetylene formed well-ordered dense overlayers which, with increasing temperature, desorbed without reaction. In striking contrast, even at 120 K, the presence of oxygen led to immediate and complete disruption of the organic layer due to abstraction of acetylenic hydrogen with formation of a disordered mixed layer containing immobile adsorbed phenylacetylide. At higher temperatures phenylacetylide underwent Glaser–Hay coupling to form highly ordered domains of diphenyldiacetylene that eventually desorbed without decomposition, leaving the bare metal surface. DFT calculations showed that, while acetylenic H abstraction was otherwise an endothermic process, oxygen adatoms triggered a reaction-initiating exothermic pathway leading to OH(a) + phenylacetylide, consistent with the experimental observations. Moreover, it was found that, with a solution of phenylacetylene in nonane and in the presence of O2, Ag particles catalyzed Glaser–Hay coupling with high selectivity. Rigorous exclusion of oxygen from the reactor strongly suppressed the catalytic reaction. Interestingly, too much oxygen lowers the selectivity toward diphenyldiacetylene. Thus, vacuum studies and theoretical calculations revealed the key role of oxygen in the reaction mechanism, subsequently borne out by catalytic studies with Ag particles that confirmed the presence of oxygen as a necessary and sufficient condition for the coupling reaction to occur. The direct relevance of model studies to a mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.


Mayo, 2017 | DOI: 10.1021/acscatal.7b00431

Energy-Sensitive Ion- and Cathode-Luminescent Radiation-Beam Monitors Based on Multilayer Thin-Film Designs


Gil-Rostra, Jorge; Ferrer, Francisco J.; Pedro Espinos, Juan; Gonzalez-Elipe, Agustin R.; Yubero, Francisco
ACS Applied Materials & Interfaces, 9 (2017) 16313-16320

ABSTRACT

A multilayer luminescent design concept is presented to develop energy sensitive radiation-beam monitors on the basis of colorimetric analysis. Each luminescent layer within the stack consists of rare-earth-doped transparent oxides of optical quality and a characteristic luminescent emission under excitation with electron or ion beams. For a given type of particle beam (electron, protons, alpha particles, etc.), its penetration depth and therefore its energy loss at a particular buried layer within the multilayer stack depend on the energy of the initial beam. The intensity of the luminescent response of each layer is proportional to the energy deposited by the radiation beam within the layer, so characteristic color emission will be achieved if different phosphors are considered in the layers of the luminescent stack. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters relevant to achieving a broad colorimetric response. Two case examples are designed and fabricated to illustrate the capabilities of these new types of detector to evaluate the kinetic energy of either electron beams of a few kilo-electron volts or a particles of alpha few mega-electron volts.


Mayo, 2017 | DOI: 10.1021/acsami.7b01175

Non-enzymatic hydrogen peroxide detection at NiO nanoporous thin film-electrodes prepared by physical vapor deposition at oblique angles


Salazar, Pedro; Rico, Victor; Gonzalez-Elipe, Agustin R.
Electrochimica Acta, 235 (2017) 534-542

ABSTRACT

In this work we report a non-enzymatic sensor for hydrogen peroxide (H2O2) detection based on nanostructured nickel thin films prepared by physical vapor deposition at oblique angles. Porous thin films deposited on ITO substrates were characterized by X-ray diffraction analysis, scanning electron microcopy (SEMs), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques such as Cyclic Voltammetry (CV) and Constant Potential Amperometry (CPA). The microstructure of the thin films consisted of inclined and separated Ni nanocolumns forming a porous thin layer of about 500 nm thickness. Prior to their use, the films surface was electrochemically modified and the chemical state studied by CV and XPS analysis. These techniques also showed that Ni2+/Ni3+ species were involved in the electrochemical oxidation and detection of H2O2 in alkaline medium. Main analytical parameters such as sensitivity (807 mA M(-1)cm(-2)), limit of detection (3.22 mu M) and linear range (0.011-2.4 mM) were obtained under optimal operation conditions. Sensors depicted an outstanding selectivity and a high stability and they were successfully used to determine H2O2 concentration in commercial antiseptic solutions.


Mayo, 2017 | DOI: 10.1016/j.electacta.2017.03.087

Improving the pollutant removal efficiency of packed-bed plasma reactors incorporating ferroelectric components


Gomez-Ramirez, Ana; Montoro-Damas, Antonio M.; Rodriguez, Miguel A.; Gonzalez-Elipe, Agustin R.; Cotrino, Jose
Chemical Engineering Journal, 314 (2017) 311-319

ABSTRACT

In this work we have studied the plasma removal of air contaminants such as methane, chloroform, toluene and acetone in two parallel plate packed-bed dielectric barrier discharge (DBD) reactors of different sizes. Removal and energy efficiencies have been determined as a function of the residence time of the contaminated air within the reactor, the kind of packed-bed material (ferroelectrics or classical dielectric materials), the frequency and the incorporation of a ferroelectric plate onto the active electrode together with the inter-electrode ferroelectric pellets filling the gap. Results at low frequency with the small reactor and the ferroelectric plate showed an enhancement in energy efficiency (e.g., it was multiplied by a factor of six and three for toluene and chloroform, respectively) and in removal yield (e.g., it increased from 22% to 52% for chloroform and from 15% to 21% for methane). Such enhancements have been attributed to the higher energy of plasma electrons and a lower reactor capacitance found for this plate-modified configuration. A careful analysis of reaction efficiencies and electron energy distributions for the different investigated conditions and the simulation of the electric field at the necks between ferroelectric/dielectric pellets complete the present study. Overall, the obtained results prove the critical role of the barrier architecture and operating conditions for an enhanced performance of pollution removal processes using DBD systems.


Abril, 2017 | DOI: 10.1016/j.cej.2016.11.065

Formation of nitrile species on Ag nanostructures supported on a-Al2O3: a new corrosion route for silver exposed to the atmosphere


Pelaez, RJ; Espinos, JP; Afonso, CN
Nanotechnology, 28 (2017) 175709

ABSTRACT

The aging of supported Ag nanostructures upon storage in ambient conditions (air and room temperature) for 20 months has been studied. The samples are produced on glass substrates by pulsed laser deposition (PLD); first a 15 nm thick buffer layer of amorphous aluminum oxide (a-Al2O3) is deposited, followed by PLD of Ag. The amount of deposited Ag ranges from that leading to a discontinuous layer up to an almost-percolated layer with a thickness of <6 nm. Some regions of the as-grown silver layers are converted, by laser induced dewetting, into round isolated nanoparticles (NPs) with diameters of up to ~25 nm. The plasmonic, structural and chemical properties of both as-grown and laser exposed regions upon aging have been followed using extinction spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The results show that the discontinuous as-grown regions are optically and chemically unstable and that the metal becomes oxidized faster, the smaller the amount of Ag. The corrosion leads to the formation of nitrile species due to the reaction between NO x species from the atmosphere adsorbed at the surface of Ag, and hydrocarbons adsorbed in defects at the surface of the a-Al2O3 layer during the deposition of the Ag nanostructures by PLD that migrate to the surface of the metal with time. The nitrile formation thus results in the main oxidation mechanism and inhibits almost completely the formation of sulphate/sulphide. Finally, the optical changes upon aging offer an easy-to-use tool for following the aging process. They are dominated by an enhanced absorption in the UV side of the spectrum and a blue-shift of the surface plasmon resonance that are, respectively, related to the formation of a dielectric overlayer on the Ag nanostructure and changes in the dimensions/features of the nanostructures, both due to the oxidation process.


Abril, 2017 | DOI: 10.1088/1361-6528/aa65c0

Multicolored Emission and Lasing in DCM-Adamantane Plasma Nanocomposite Optical Films


Alcaire, M; Cerdan, L; Zamarro, FL; Aparicio, FJ; Gonzalez, JC; Ferrer, FJ; Borras, A; Espinos, JP; Barranco, A
ACS Applied Materials & Interfaces, 9 (2017) 8948-8959

ABSTRACT

We present a low-temperature versatile protocol for the fabrication of plasma nanocomposite thin films to act as tunable emitters and optical gain media. The films are obtained by the remote plasma-assisted deposition of a 4-(dicyano-methylene)-2-methy1-6-(4-dimethylamino-styry1)-4Hpyran (DCM) laser dye alongside adamantane. The experimental parameters that determine the concentration of the dye in the films and their optical properties, including light absorption, the refractive index, and luminescence, are evaluated. Amplified spontaneous emission experiments in the DCM/adamantane nano composite waveguides show the improvement of the copolymerized nano composites' properties compared to films that were deposited with DCM as the sole precursor. Moreover, one-dimensional distributed feed-back laser emission is demonstrated and characterized in some of the nanocomposite films that are studied. These results open new paths for the optimization of the optical and lasing properties of plasma nanocomposite polymers, which can be straightforwardly integrated as active components in optoelectronic devices.


Marzo, 2017 | DOI: 10.1021/acsami.7b01534

Strong Quantum Confinement and Fast Photoemission Activation in CH3NH3PbI3 Perovskite Nanocrystals Grown within Periodically Mesostructured Films


Miguel Anaya; Andrea Rubino; Teresa Cristina Rojas; Juan Francisco Galisteo-López; Mauricio Ernesto Calvo; Hernán Míguez
Advanced Optical Materials

ABSTRACT

In this Communication, a synthetic route is demonstrated to obtain stabilized MAPbI3 nanocrystals embedded in thin metal oxide films that display well-defined and adjustable quantum confinement effects over a wide range of 0.34 eV. Mesostructured TiO2 and SiO2 films displaying an ordered 3D pore network are prepared by evaporation-induced self-assembly of a series of organic supramolecular templates in the presence of metal oxide precursors. The pores in the inorganic films obtained after thermal annealing are then used as nanoreactors to synthesize MAPbI3crystallites with narrow size distribution and average radius comprised between 1 and 4 nm, depending on the template of choice. Both the static and dynamic photoemission properties of the ensemble display features distinctive of the regime of strong quantum confinement. Photoemission maps demonstrate that the spectral and intensity properties of the luminescence extracted from the perovskite quantum dot loaded films are homogeneous over squared centimeters areas. At variance with their bulk counterparts, constant emission intensity is reached in time scales at least four orders of magnitude shorter.


Marzo, 2017 | DOI: 10.1002/adom.201601087

Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings


Dominguez-Meister, S; Rojas, TC; Brizuela, M; Sanchez-Lopez, JC
Science and Tecnology of Advances Materials, 18 (2017) 1

ABSTRACT

Tribological coatings made of MoS2 and WSe2 phases and their corresponding combinations with tungsten carbide (WC) were prepared by non-reactive magnetron sputtering of individual targets of similar composition. A comparative tribological analysis of these multiphase coatings was done in both ambient air (30-40% relative humidity, RH) and dry nitrogen (RH<7%) environments using the same tribometer and testing conditions. A nanostructural study using advanced transmission electron microscopy of the initial coatings and examination of the counterfaces after the friction test using different analytical tools helped to elucidate what governs the tribological behavior for each type of environment. This allowed conclusions to be made about the influence of the coating microstructure and composition on the tribological response. The best performance obtained with a WSe x film (specific wear rate of 2 x 10(-8) mm(3) N(-1)m(-1) and a friction coefficient of 0.03-0.05) was compared with that of the well-established MoS2 lubricant material.


Marzo, 2017 | DOI: 10.1080/14686996.2016.1275784

Antibacterial response of titanium oxide coatings doped by nitrogen plasma immersion ion implantation


Esparza, J; Fuentes, GF; Bueno, R; Rodriguez, R; Garcia, JA; Vitas, AI; Rico, V; Gonzalez-Elipe, AR
Surface and Coatings Technology, 314 (2017) 67-71

ABSTRACT

Plasma immersion ion implantation technology has been utilized to enhance the photocatalytic activity of the anatase phase of TiO2 thin films deposited by cathodic arc evaporation PVD. The main objective of this study is to shift the light absorbance of the titania in order to obtain antibacterial activity under visible light irradiation. TiO2 thin films, deposited on polished stainless steel AISI 304 and silicon wafers, were implanted with nitrogen ions (N+/N2+) at 20 kV energy and different temperatures between 250 and 350 °C. The antibacterial activity of nitrogen implanted titania coatings has been monitored for Escherichia coli under visible light irradiation. Additionally ultra violet/visible spectrophotometry tests have been carried out to measure the changes in the light absorbance of the doped films. Further characterization has been performed, including X-ray photoelectron spectroscopy, X-ray diffraction and glow discharge optical emission spectrometry. As a result of Nitrogen implantation, the light absorption peak shifted from ultra violet region (UV-A) to visible wavelength range, which led to an increase of the antibacterial efficacy under visible light irradiation.


Marzo, 2017 | DOI: 10.1016/j.surfcoat.2016.11.002

On the effect of wall slip on the determination of the yield stress of magnetorheological fluids


Caballero-Hernandez, J; Gomez-Ramirez, A; Duran, JDG; Gonzalez-Caballero, F; Zubarev, AY; Lopez-Lopez, MT
Applied Rheology, 27 (2017) 15001 (8 pages)

ABSTRACT

We study the effect of wall slip on the measured values of the yield stress of magnetorheological (MR) fluids. For this aim we used a rheometer provided with parallel-plate geometries of two types, distinguished by having smooth or rough surfaces. We found that wall slip led to the underestimation of the yield stress when measuring geometries with smooth surfaces were used, and that this underestimation was more pronounced for the static than for the dynamic yield stress. Furthermore, we analysed the effect that both irreversible particle aggregation due to colloidal interactions and reversible magnetic fieldinduced particle aggregation had on the underestimation provoked by wall slip. We found that the higher the degree of aggregation the stronger the underestimation of the yield stress. At low intensity of the applied magnetic field irreversible particle aggregation was dominant and, thus, the underestimation of the yield stress was almost negligible for well-dispersed MR fluids, whereas it was rather pronounced for MR fluids suffering from irreversible aggregation. As the magnetic field was increased the underestimation of the yield stress became significant even for the best dispersed MR fluid.


Marzo, 2017 | DOI: 10.3933/ApplRheol-27-15001

Reliability of new poly (lactic-co-glycolic acid) membranes treated with oxygen plasma plus silicon dioxide layers for pre-prosthetic guided bone regeneration processes


Castillo-Dali, G; Castillo-Oyague, R; Batista-Cruzado, A; Lopez-Santos, C; Rodriguez-Gonzalez-Elipe, A; Saffar, JL; Lynch, CD; Gutierrez-Perez, JL; Torres-Lagares, D
Medicina Oral Patología Oral y Cirugia Oral, 22 (2017) E242-E250

ABSTRACT

Background: The use of cold plasmas may improve the surface roughness of poly(lactic-co-glycolic) acid (PLGA) membranes, which may stimulate the adhesion of osteogenic mediators and cells, thus accelerating the biodegradation of the barriers. Moreover, the incorporation of metallic-oxide particles to the surface of these membranes may enhance their osteoinductive capacity. Therefore, the aim of this paper was to evaluate the reliability of a new PLGA membrane after being treated with oxygen plasma (PO2) plus silicon dioxide (SiO2) layers for guided bone regeneration (GBR) processes. 
Material and Methods: Circumferential bone defects (diameter: 11 mm; depth: 3 mm) were created on the top of eight experimentation rabbits' skulls and were randomly covered with: (1) PLGA membranes (control), or (2) PLGA/ PO2/SiO2 barriers. The animals were euthanized two months afterwards. A micromorphologic study was then performed using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone, concentration of osteoclasts, and intensity of ostheosynthetic activity were assessed and compared with those of the original bone tissue. The Kruskal-Wallis test was applied for between-group com asignificance level of a=0.05 was considered. 
Results: The PLGA/ PO2/SiO2 membranes achieved the significantly highest new bone formation, length of miner-alised bone, concentration of osteoclasts, and ostheosynthetic activity. The percentage of regenerated bone supplied by the new membranes was similar to that of the original bone tissue. Unlike what happened in the control group, PLGA/PO2/SiO2 membranes predominantly showed bone layers in advanced stages of formation. Conclusions: The addition of SiO2 layers to PLGA membranes pre-treated with PO2 improves their bone-regeneration potential. Although further research is necessary to corroborate these conclusions in humans, this could be a promising strategy to rebuild the bone architecture prior to rehabilitate edentulous areas.


Marzo, 2017 | DOI: 10.4317/medoral.21512

High vacuum synthesis and ambient stability of bottom-up graphene nanoribbons


Fairbrother, A; Sanchez-Valencia, JR; Lauber, B; Shorubalko, I; Ruffieux, P; Hintermann, T; Fasel, R
Nanoscale, 9 (2017) 2785-2792

ABSTRACT

Carbon-based nanomaterials such as graphene are at a crucial point in application development, and their promising potential, which has been demonstrated at the laboratory scale, must be translated to an industrial setting for commercialization. Graphene nanoribbons in particular overcome one limitation of graphene in some electronic applications because they exhibit a sizeable bandgap. However, synthesis of bottom-up graphene nanoribbons is most commonly performed under ultra-high vacuum conditions, which are costly and difficult to maintain in a manufacturing environment. Additionally, little is known about the stability of graphene nanoribbons under ambient conditions or during transfer to technologically relevant substrates and subsequent device processing. This work addresses some of these challenges, first by synthesizing bottom-up graphene nanoribbons under easily obtained high vacuum conditions and identifying water and oxygen as the residual gases responsible for interfering with proper coupling during the polymerization step. And second, by using Raman spectroscopy to probe the stability of nanoribbons during storage under ambient conditions, after transfer to arbitrary substrates, and after fabrication of field-effect transistor devices, which shows structurally intact nanoribbons even several months after synthesis. These findings demonstrate the potential of graphene nanoribbon technologies by addressing some limitations which might arise in their commercialization.


Febrero, 2017 | DOI: 10.1039/C6NR08975E

Cholesterol biosensing with a polydopamine-modified nanostructured platinum electrode prepared by oblique angle physical vacuum deposition


Martin, M; Salazar, P; Alvarez, R; Palmero, A; Lopez-Santos, C; Gonzalez-Mora, JL; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 240 (2017) 37-45

ABSTRACT

This paper reports a novel cholesterol biosensor based on nanostructured platinum (Pt) thin films prepared by Magnetron Sputtering (MS) in an oblique angle (OAD) configuration. Pt thin films were deposited onto a gold screen-printed electrode and characterized using Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Cyclic Voltammetry (CV), X-ray Photo-electron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and wetting analysis. Our results confirmed that the film is highly porous and formed by tilted nanocolumns, with an inclination of around 40 degrees and a total thickness of 280 nm. XRD and CV analysis confirmed the polycrystalline nature of the Pt thin film. Cholesterol oxidase (ChOx) was covalently immobilized using a bioinspired polymer, polydopamine (PDA), via Schiff base formation and Michael-type addition. After being immobilized, ChOx displayed apparent activation energy of 34.09 kJ mol(-1) and Michaelis constant (K-M) values of 34.09 kJ mol(-1) and 3.65 mM, respectively, confirming the high affinity between ChOx and cholesterol and the excellent ability of the PDA film for immobilizing biological material without degradation. Under optimized working conditions the developed biosensor presented a sensitivity of 14.3 mA M(-1)cm(-2) (R-2:0.999) with a linear range up to 0.5 mM and a limit of detection of 10.5 mu M (S/N= 3). Furthermore, the biosensor exhibited a fast response (<8 s), good anti-interference properties and high stability after relatively long-term storage (2 months). 


Febrero, 2017 | DOI: 10.1016/j.snb.2016.08.092

Fabrication of black-gold coatings by glancing angle deposition with sputtering


Vitrey, A; Alvarez, R; Palmero, A; Gonzalez, MU; Garcia-Martin, JM
Beilstein Journal of Nanotechnology, 8 (2017) 434–439

ABSTRACT

The fabrication of black-gold coatings using sputtering is reported here. Glancing angle deposition with a rotating substrate is needed to obtain vertical nanostructures. Enhanced light absorption is obtained in the samples prepared in the ballistic regime with high tilt angles. Under these conditions the diameter distribution of the nanostructures is centered at about 60 nm and the standard deviation is large enough to obtain black-metal behavior in the visible range.


Febrero, 2017 | DOI: 10.3762/bjnano.8.46

Preparation and Optimization of Fluorescent Thin Films of Rosamine-SiO2/TiO2 Composites for NO2 Sensing


Guillen, MG; Gamez, F; Suarez, B; Queiros, C; Silva, AMG; Barranco, A; Sanchez-Valencia, JR; Pedrosa, JM; Lopes-Costa, T
Materials, 10 (2017) art 124

ABSTRACT

The incorporation of a prototypical rosamine fluorescent dye from organic solutions into transparent and microstructured columnar TiO2 and SiO2 (MO2) thin films, prepared by evaporation at glancing angles (GAPVD), was evaluated. The aggregation of the adsorbed molecules, the infiltration efficiency and the adsorption kinetics were studied by means of UV-Vis absorption and fluorescence spectroscopies. Specifically, the infiltration equilibrium as well as the kinetic of adsorption of the emitting dye has been described by a Langmuir type adsorption isotherm and a pseudosecond order kinetic model, respectively. The anchoring mechanism of the rosamine to the MO2 matrix has been revealed by specular reflectance Fourier transform infrared spectroscopy and infiltration from aqueous solutions at different pH values. Finally, the sensing performance towards NO2 gas of optimized films has been assessed by following the changes of its fluorescence intensity revealing that the so-selected device exhibited improved sensing response compared to similar hybrid films reported in the literature.


Febrero, 2017 | DOI: 10.3390/ma10020124

Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions


Arzac, G. M.; Montes, O.; Fernandez, A.
Applied Catalysis B-Envionmental, 201 (2017) 391-399

ABSTRACT

We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. beta-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5 wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5 wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5 wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystsi surface.


Enero, 2017 | DOI: 10.1016/j.apcatb.2016.08.042

Regenerative Endodontic Procedures: A Perspective from Stem Cell Niche Biology


M. Marí-Beffa, J.J. Segura-Egea, A. Díaz-Cuenca
Journal of Endodontics, 43 (2017) 52-62

ABSTRACT

Introduction

Endodontics uses cell therapy strategies to treat pulpal and periapical diseases. During these therapies, surgeons aim to reconstruct the natural microenvironments that regulate the activity of dental stem cells.

Methods

We searched for more than 400 articles in PubMed using key words from regenerative endodontics and dental stem cell biology. In 268 articles, we reviewed what factors may influence histologic results after preclinical dental treatments that use regenerative endodontic procedures after pulpectomy.

Results

Several factors, such as the origin of stem cells, the biomimicry of scaffolds used, and the size of lesions, are considered to influence the histologic appearance of the regenerated pulp-dentin complex after treatments. Information is accumulating on transcription factors that generate the pulp-dentin complex and survival/trophic factors that would benefit niche recovery and histologic results.

Conclusions

In this article, we discuss the noninterchangeability of stem cells, the influence of dentin-entrapped molecule release on pulp regeneration and survival of stem cells, and the need of positional markers to assess treatments histologically. The ex vivo amplification of appropriate dental stem cells, the search for scaffolds storing the molecular diversity entrapped in the dentin, and the use of positional transcription factors as histologic markers are necessary to improve future preclinical experiments.


Enero, 2017 | DOI: 10.1016/j.joen.2016.09.011

Optical Gas Sensing of Ammonia and Amines Based on Protonated Porphyrin/TiO2 Composite Thin Films


Castillero, Pedro; Roales, Javier; Lopes-Costa, Tania; Sanchez-Valencia, Juan R.; Barranco, Angel; Gonzalez-Elipe, Agustin R.; Pedrosa, Jose M.
Sensors, 17 (2017) 24

ABSTRACT

Open porous and transparent microcolumnar structures of TiO2 prepared by physical vapour deposition in glancing angle configuration (GLAD-PVD) have been used as host matrices for two different fluorescent cationic porphyrins, 5-(N-methyl 4-pyridyl)-10,15,20-triphenyl porphine chloride (MMPyP) and meso-tetra (N-methyl 4-pyridyl) porphine tetrachloride (TMPyP). The porphyrins have been anchored by electrostatic interactions to the microcolumns by self-assembly through the dip-coating method. These porphyrin/TiO2 composites have been used as gas sensors for ammonia and amines through previous protonation of the porphyrin with HCl followed by subsequent exposure to the basic analyte. UV-vis absorption, emission, and time-resolved spectroscopies have been used to confirm the protonation-deprotonation of the two porphyrins and to follow their spectral changes in the presence of the analytes. The monocationic porphyrin has been found to be more sensible (up to 10 times) than its tetracationic counterpart. This result has been attributed to the different anchoring arrangements of the two porphyrins to the TiO2 surface and their different states of aggregation within the film. Finally, there was an observed decrease of the emission fluorescence intensity in consecutive cycles of exposure and recovery due to the formation of ammonium chloride inside the film.


Enero, 2017 | DOI: 10.3390/s17010024



2016


Non-Enzymatic Glucose Sensors Based on Nickel Nanoporous Thin Films Prepared by Physical Vapor Deposition at Oblique Angles for Beverage Industry Applications


Salazar, P; Rico, V; Gonzalez-Elipe, AR
Journal of the Electrochemical Society, 163 (14) (2016) B704-B709

ABSTRACT

Nickel nanoporous thin films deposited on Indium tin oxide conductive plates have been prepared by physical vapor deposition in an oblique angle configuration. The scanning electron microscopy characterization of these films revealed a microstructure formed by tilted nanocolumns of ca. 40-60 nm of diameter inclined by ca. 26 degrees with respect to the normal. These highly porous films had ca. 30% of void space and provided a large exposed area and outstanding diffusion properties for sensor applications. X-ray diffraction analysis confirmed the deposition of metallic nickel, while Raman and X-ray photoelectron spectroscopies demonstrated that electrochemically treated films presented an oxi/hydroxide outer layer that is the active phase for glucose sensing. The activated electrodes had a high sensitivity (2.05 A M-1 cm(-2)), an excellent coefficient of determination (R-2: 0.999), an outstanding reproducibility (3.2%) and a detection limit of 0.34 mu M. Their glucose selectivity was excellent with regard to common electroactive interferences and other sugars found in agro-alimentary products. Tests carried out with commercial beverages proved the reliability of these electrodes for glucose analysis in real conditions.


Diciembre, 2016 | DOI: 10.1149/2.1241614jes

Stoichiometric Control of SiOx Thin Films Grown by Reactive Magnetron Sputtering at Oblique Angles


Garcia-Valenzuela, A; Alvarez, R; Lopez-Santos, C; Ferrer, FJ; Rico, V; Guillen, E; Alcon-Camas, M; Escobar-Galindo, R; Gonzalez-Elipe, AR; Palmero, A
Plasma Processes and Polymers, 13 (2016) 1242-1248

ABSTRACT

The deposition of SiOx (x <= 2) compound thin films by the reactive magnetron sputtering technique at oblique angles is studied from both theoretical and experimental points of view. A simple mathematical formula that links the film stoichiometry and the deposition conditions is deduced. Numerous experiments have been carried out to test this formula at different deposition pressures and oblique angle geometries obtaining a fairly good agreement in all studied conditions. It is found that, at low deposition pressures, the proportion of oxygen with respect to silicon in the film increases a factor of similar to 5 when solely tilting the film substrate with respect to the target, whereas at high pressures the film stoichiometry depends very weakly on the tilt angle. This behavior is explained by considering the fundamental processes mediating the growth of the film by this technique.


Diciembre, 2016 | DOI: 10.1002/ppap.201600077

Glutamate microbiosensors based on Prussian Blue modified carbon fiber electrodes for neuroscience applications: In-vitro characterization


Salazar, P; Martin, M; O'Neill, RD; Gonzalez-Mora, JL
Sensors and Actuators B: Chemical, 235 (2016) 117-125

ABSTRACT

Herein we report a Prussian Blue modified carbon fiber electrode (CFE/PB) to be used in microbiosensors for glutamate monitoring in physiological applications as an alternative to the classical Pt and Pt-Ir transducers. Their low dimensions (∼250 μm CFE length and ∼10 μm diameter) are advantageous for measuring in living tissues. In addition, PB-modified microelectrodes allow the detection of enzyme-generated hydrogen peroxide at a low applied potential (∼0.0 V against SCE), contrasting the high potential used in many previous designs (∼0.7 V), decreasing the endogenous interference contributions. Moreover, the electrosynthesized polymer, poly-o-phenylenediamine (PoPD), was used to improve biosensor stability and selectivity. CFE/PB was conveniently characterized using impedance, Raman and XPS spectroscopies. Optimization of the fabrication procedure and analytical conditions is described, including activation of CFE/PB, enzyme enrichment, cross-linking, stabilization and anti-interference. A range of analytical parameters were also characterized such as sensitivity, limit of detection, linear range, and enzymatic loading. Finally, an optimized biosensor displaying a linear sensitivity of 135 ± 2 nA μM−1 cm−2 (n = 3), LOD of <2 μM, linear range up to 150 μM and effectively free of interference, is proposed as a suitable candidate for in-vivo glutamate monitoring in the central nervous system.


Noviembre, 2016 | DOI: 10.1016/j.snb.2016.05.057

Tailor-made preparation of Co-C, Co-B, and Co catalytic thin films using magnetron sputtering: insights into structure-composition and activation effects for catalyzed NaBH4 hydrolysis


Paladini, M; Godinho, V; Arzac, GM; de Haro, MCJ; Beltran, AM; Fernandez, A
RSC Advances, 6 (2016) 108611-108620

ABSTRACT

The magnetron sputtering (MS) methodology is a powerful tool for tailor-made fabrication of Co-based thin film catalysts with controlled microstructures and compositions for sodium borohydride (SBH) hydrolysis. In particular, Co-C catalysts were tested in this reaction and compared to Co-B and Co catalyst coatings. The microstructural and chemical analyses by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS) were used to characterize a complete library of thin film catalysts. Pure Co materials were characterized by their nanocrystalline microstructure, and grain refinement was achieved via an increase in the deposition pressure. The incorporation of boron or carbon via co-deposition results in amorphization and dispersion of the active metallic Co phase. The composition can be tuned while keeping a controlled microstructure, and a comparison of activity at 25 degrees C was performed on catalysts deposited on Ni foam substrates. A comparison of the initial activities showed that the Co-B samples were more active than the Co-C samples because of electronic effects. However, a strong activation was found for the Co-C catalysts after the first use. This effect was dependent upon the incorporation of cobalt boride (CoxB) species on the catalysts' surface, as shown by XPS. After the first several uses, the activity of the Co-C samples (values up to 2495 mL min(-1) g(catalyst)(-1)) were as high as that of fresh Co-B, and the surface composition of both the catalysts was similar. This activation was not observed for the pure Co and was very weak for the Co-B catalysts. The use of polymeric (PTFE) substrates (flexible membranes) illustrated the versatility of the methodology to obtain catalytic membranes and allowed for a TEM microstructural analysis at the nanoscale. Catalytic activities at 60 degrees C were as high as 16.7 and 20 L min(-1) g(Co)(-1) for the Co-C and Co-B membranes, respectively. We determined the optimized conditions to increase the catalytic activity of Co-based coatings prepared via magnetron sputtering.


Noviembre, 2016 | DOI: 10.1039/c6ra23171c

Characterization and Validation of a-Si Magnetron-Sputtered Thin Films as Solid He Targets with High Stability for Nuclear Reactions


Godinho, V; Ferrer, FJ; Fernandez, B; Caballero-Hernandez, J; Gomez-Camacho, J; Fernandez, A
ACS Omega, 1 (2016) 1229-1238

ABSTRACT

In this work, we present our magnetron sputtering based methodology to produce amorphous silicon coatings with closed porosity, as a strategy to fabricate solid helium targets, in the form of supported or self-supported thin films, for nuclear reactions. We show how by changing the He working pressure it is possible to obtain highly porous homogeneous structures incorporating different He amounts. These porous coatings (a-Si: He) are very reproducible from run to run, and the high He amount incorporated makes them excellent candidates for solid He targets. The possibility of producing self-supported films is illustrated here, and its potential use in inverse kinematics experiments with radioactive beams is shown through the dispersion in forward geometry of a stable Li-6 beam. Also the elastic scattering cross-sections for proton from helium were determined using an a-Si: He coating. The results agree well with the ones reported in the literature. These two examples validate our coatings as good candidates to be used as solid He targets in nuclear reactions. The stability of He inside the coatings, fundamental for its use as solid He targets, was investigated, both over time and after irradiation. The coatings proved to be very stable, and the amount of He inside the pores remains unaltered at least 2 years after deposition and after high irradiation fluence (5 x 10(17) particles/cm(2); with a dose rate of 5 x 10(12) particles/(cm(2) s)).


Noviembre, 2016 | DOI: 10.1021/acsomega.6b00270

High-Rate Deposition of Stoichiometric Compounds by Reactive Magnetron Sputtering at Oblique Angles


Rafael Alvarez, Aurelio Garcia-Valenzuela, Carmen Lopez-Santos, Francisco J. Ferrer, Victor Rico, Elena Guillen, Mercedes Alcon-Camas, Ramon Escobar-Galindo, Agustin R. Gonzalez-Elipe, Alberto Palmero
Plasma Processes and Polymers, 13 (2016) 571-576

ABSTRACT

Target poisoning in reactive magnetron sputtering deposition of thin films is an undesired phenomenon, well known for causing a drastic fall of the process efficiency. We demonstrate that when this technique is operated at oblique angles, films with composition raging from pure metallic to stoichiometric compound can be grown in non-poisoned conditions, thus avoiding most of the associated drawbacks. We have employed amorphous TiOx, although the presented results can be easily extrapolated to other materials and conditions. It is found that the proposed method improves 400% the growth rate of TiO2 thin films.


Octubre, 2016 | DOI: 10.1002/ppap.201600019

Cathode and ion-luminescence of Eu:ZnO thin films prepared by reactive magnetron sputtering and plasma decomposition of non-volatile precursors


Gil-Rostra, J; Ferrer, FJ; Martin, IR; Gonzalez-Elipe, AR; Yubero, F
Journal of Luminescence, 178 (2016) 139-146

ABSTRACT

This paper reports the luminescent behavior of Eu:ZnO thin films prepared by an one-step procedure that combines reactive magnetron sputtering deposition of ZnO with the plasma activated decomposition of a non-volatile acetylacetonate precursor of Eu sublimated in an effusion cell. Chemical composition and microstructure of the Eu:ZnO thin films have been characterized by several methods and their photo-, cathode- and ion-luminescent properties studied as a function of Eu concentration. The high transparency and well controlled optical properties of the films have demonstrated to be ideal for the development of cathode- and ion- luminescence sensors.


Octubre, 2016 | DOI: 10.1016/j.jlumin.2016.01.034

Stabilization of catalyst particles against sintering on oxide supports with high oxygen ion lability exemplified by Ir-catalyzed decomposition of N2O


Yentekakis, IV; Goula, G; Panagiotopoulou, P; Kampouri, S; Taylor, MJ; Kyriakou, G; Lambert, RM
Applied Catalysis B-Environmental, 192 (2016) 357-364

ABSTRACT

Iridium nanoparticles deposited on a variety of surfaces exhibited thermal sintering characteristics that were very strongly correlated with the lability of lattice oxygen in the supporting oxide materials. Specifically, the higher the lability of oxygen ions in the support, the greater the resistance of the nanoparticles to sintering in an oxidative environment. Thus with gamma-Al2O3 as the support, rapid and extensive sintering occurred. In striking contrast, when supported on gadolinia-ceria and alumina-ceria-zirconia composite, the Ir nanoparticles underwent negligible sintering. In keeping with this trend, the behavior found with yttria-stabilized zirconia was an intermediate between the two extremes. This resistance, or lack of resistance, to sintering is considered in terms of oxygen spillover from support to nanoparticles and discussed with respect to the alternative mechanisms of Ostwald ripening versus nanoparticle diffusion. Activity towards the decomposition of N2O, a reaction that displays pronounced sensitivity to catalyst particle size (large particles more active than small particles), was used to confirm that catalytic behavior was consistent with the independently measured sintering characteristics. It was found that the nanoparticle active phase was Ir oxide, which is metallic, possibly present as a capping layer. Moreover, observed turnover frequencies indicated that catalyst-support interactions were important in the cases of the sinter-resistant systems, an effect that may itself be linked to the phenomena that gave rise to materials with a strong resistance to nanoparticle sintering. 


Septiembre, 2016 | DOI: 10.1016/j.apcatb.2016.04.011

Laser Treatment of Nanoparticulated Metal Thin Films for Ceramic Tile Decoration


Rico, VJ; Lahoz, R; Rey-Garcia, F; Yubero, F; Espinos, JP; de la Fuente, GF; Gonzalez-Elipe, AR
Applied Materials & Interfaces, 8 (2016) 24880-24886

ABSTRACT

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV–vis–near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.


Septiembre, 2016 | DOI: 10.1021/acsami.6b07469

Isotope labelling to study molecular fragmentation during the dielectric barrier discharge wet reforming of methane


Montoro-Damas, AM; Gomez-Ramirez, A; Gonzalez-Elipe, AR; Cotrino, J
Journal of Power Sources, 325 (2016) 501-505

ABSTRACT

Isotope labelling is used to study the wet plasma reforming of methane in a dielectric barrier discharge reactor using D2O and CH4 as reactants. Besides the formation of CO and hydrogen as main products, different partitions of H and D atoms are found in the hydrogen (i.e., Hz, HD, D-2), methane (i.e., CH4, CH3D and CH2D2) and water (D2O, DHO) molecules detected by mass spectrometry as outlet gases of the plasma process. The effect of operating parameters such as applied current, residence time and the addition of oxygen to the reaction mixture is correlated with the H/D distribution in these molecules, the overall reaction yield and the energetic efficiency of the process. The results prove the plasma formation of intermediate excited species that rendering water and methane instead of CO and hydrogen greatly contribute to decrease the overall energy efficiency of the reforming process.


Septiembre, 2016 | DOI: 10.1016/j.jpowsour.2016.06.028

Reduced graphene oxide-carboxymethylcellulose layered with platinum nanoparticles/PAMAM dendrimer/magnetic nanoparticles hybrids. Application to the preparation of enzyme electrochemical biosensors


Borisova, B; Sanchez, A; Jimenez-Falcao, S; Martin, M; Salazar, P; Parrado, C; Pingarron, JM; Villalonga, R
Sensors and Actuators B-Chemical, 232 (2016) 84-90

ABSTRACT

The assembly of a novel layer-by-layer biosensor architecture using hybrid nanomaterials is explored for the construction of an amperometric enzyme biosensors. The nanostructured sensing interface was prepared with poly(dopamine)-modified magnetic nanoparticles which were covalently coated with four-generation ethylenediamine core polyamidoamine G-4 dendrimers and further decorated with platinum nanoparticles. This nanohybrid was fully characterized and further layered on glassy carbon electrodes coated with a graphene oxide-carboxymethylcellulose hybrid nanomaterial through electrostatic interactions. The nanostructured surface was then employed as scaffold for the covalent immobilization of the enzyme xanthine oxidase through a glutaraldehyde-mediated cross-linking. The enzyme electrode allowed the amperometric detection of xanthine in the 50 nM-12 mu M range, with a high sensitivity of 140 mA/M cm(2) and low detection limit of 13 nM. The biosensor exhibited high reproducibility and repeatability, and was successfully tested for the quantification of xanthine in fish samples. 


Septiembre, 2016 | DOI: 10.1016/j.snb.2016.02.106

Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles


Lopez-Santos, C; Alvarez, R; Garcia-Valenzuela, A; Rico, V; Loeffler, M; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 27 (2016) 395702

ABSTRACT

Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2.


Septiembre, 2016 | DOI: 10.1088/0957-4484/27/39/395702

Metallization of ceramic substrates by laser induced decomposition of coordination complexes


Rico, V; Lopez-Gascon, C; Espinos, JP; Lahoz, R; Laguna, M; Gonzalez-Elipe, AR; de la Fuente, GF
Journal of the European Ceramic Society, 36 (2016) 2831-2836

ABSTRACT

This work describes an in-situ Nd:YAG laser-assisted coating method to modify industrial glazed ceramic surfaces. The method makes use of a Cu polymer coordination complex, transformed via 1064 nm continuos wave (cw) laser irradiation, into a lustre-type glassy coating covering the ceramic substrate. The obtained coatings, with typical thicknesses ranging between 4 and 14 μm, become integrated onto the ceramic glaze via a sharp interface, as found by SEM observation. Diffuse Reflectance UV-vis spectroscopy shows that the lustre effect arises from surface plasmon resonant effects associated to the formation of nanometric size Cu particles dispersed throughout the glaze coating. This was confirmed by XPS analysis and other techniques showing that the laser decomposition treatment induces the redox transformation of the Cu (II) complexes, present in the original precursor, into reduced Cu (0) nanoparticles.


Septiembre, 2016 | DOI: 10.1016/j.jeurceramsoc.2016.04.016

Effect of Nickel and Magnesium on the Electrochemical Behavior of AA 1050 Alloys in Nitric Acid Solution


Garcia-Garcia, FJ; Skeldon, P; Thompson, GE
Journal of the Electrochemical Society, 163 (9) (2016) C593-C601

ABSTRACT

The study investigates the influence of nickel and magnesium additions to AA 1050 aluminum alloy on the electrochemical behavior of the alloy in nitric acid solution under conditions relevant to the lithographic and electronic industries. Magnesium and nickel additions are of interest, since they can improve the alloy properties for the printing process by improving reverse bending fatigue strength and thermal softening resistance, while nickel may provide uniform pitting during electrograining. Scanning electron microscopy was used to characterize the resulting surface morphologies. The addition of nickel led to an increase in the pitting and corrosion potentials; additionally, it reduced the rate of dissolution of intermetallic particles during anodic polarization and increased the rate of aluminum dissolution during cathodic polarization. In contrast, the addition of magnesium had negligible influence on the open circuit and pitting behaviors, since the magnesium is retained in solid solution and has negligible influence on the cathodic behavior of intermetallic particles, which dominate the corrosion behavior.


Septiembre, 2016 | DOI: 10.1149/2.1181609jes

Timing of calcium nitrate addition affects morphology, dispersity and composition of bioactive glass nanoparticles


Zheng, K; Taccardi, N; Beltran, AM; Sui, BY; Zhou, T; Marthala, VRR; Hartmann, M; Boccaccini, AR
RSC Advances, 6 (2016) 95101-95111

ABSTRACT

Bioactive glass nanoparticles (BGN) are promising materials for a number of biomedical applications. Many parameters related to the synthesis of BGN using sol–gel methods can affect their characteristics. In this study, the influence of timing of calcium nitrate (calcium precursor) addition during processing on BGN characteristics was investigated. The results showed that the addition timing could affect the morphology, dispersity and composition of BGN. With delayed addition of calcium nitrate, larger, more regular and better dispersed BGN could be synthesized while the gap between nominal and actual compositions of BGN was widened. However, the addition timing had no significant influence on structural characteristics, as BGN with different addition-timing of calcium nitrate exhibited similar infrared spectra and amorphous nature. The results also suggested that monodispersed BGN could be synthesized by carefully controlling the addition of calcium nitrate. The synthesized monodispersed BGN could release Si and Ca ions continuously for up to at least 14 days. They also showed in vitro bioactivity and non-cytotoxicity towards rat bone marrow-derived mesenchymal stem cells (rBMSCs). In conclusion, the timing of calcium precursor addition is an essential parameter to be considered when producing BGN which should exhibit monodisperse characteristics for biomedical applications.


Septiembre, 2016 | DOI: 10.1039/C6RA05548F

Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen


Arzac, G. M.; Ramirez-Rico, J.; Gutierrez-Pardo, A.; Jimenez de Haro, M. C.; Hufschmidt, D.; Martinez-Fernandez, J.; Fernandez, A.
RSC Advances, 6 (2016) 66373-66384

ABSTRACT

Catalytic hydrogen combustion was studied with H-2/air mixtures in conditions that simulate the H-2 concentration of the exhaust gases from fuel cells (3-4% v/v H-2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monolith's outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min(-1) H-2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25-1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H-2 in air) and in powder form in kinetic conditions for comparative purposes.


Septiembre, 2016 | DOI: 10.1039/c6ra09127j

Effect of TiO2-Pd and TiO2-Ag on the photocatalytic oxidation of diclofenac, isoproturon and phenol


Espino-Estevez, MR; Fernandez-Rodriguez, C; Gonzalez-Diaz, OM; Arana, J; Espinos, JP; Ortega-Mendez, JA; Dona-Rodriguez, JM
Chemical Engineering Journal, 298 (2016) 82-95

ABSTRACT

The effects of silver and palladium metals on the photocatalytic degradation of diclofenac sodium salt (DCF), isoproturon (IP) and phenol (PHL) in water over lab-made TiO2 synthesized following a sol-gel method were investigated. Silver and palladium catalysts were prepared by photodeposition at 1 wt.% of loading metal. The resulting materials were characterized through BET, XRD, TEM, SEM, XPS and DRS-UV-Vis. The photodeposition test conditions of both metals determined their final oxidation state, with reduced particles of palladium and silver as well as silver oxides found on the catalysts. The results showed that the type of metal had different effects on the photodegradation mechanism depending on the nature of the pollutants. Accordingly, the highest degradation rate for IP and DCF was obtained when using the catalyst photodeposited with palladium and for PHL the catalyst photodeposited with silver. The photodegradation intermediates of PHL, DCF and IP were also identified.


Agosto, 2016 | DOI: 10.1016/j.cej.2016.04.016

Effects of electronic and nuclear stopping power on disorder induced in GaN under swift heavy ion irradiation


Moisy, F; Sall, M; Grygiel, C; Balanzat, E; Boisserie, M; Lacroix, B; Simon, P; Monnet, I
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 381 (2016) 39-44

ABSTRACT

Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm−1, 300 cm−1 and 670 cm−1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm−1observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).


Agosto, 2016 | DOI: 10.1016/j.nimb.2016.05.024

Synthesis, characterization and performance of robust poison resistant ultrathin film yttria stabilized zirconia nickel anodes for application in solid electrolyte fuel cells


Garcia-Garcia, FJ; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Lambert, RM
Journal of Power Sources, 324 (2016) 679-686

ABSTRACT

We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.


Julio, 2016 | DOI: 10.1016/j.jpowsour.2016.05.124

In vitro stimulation of MC3T3-E1cells and sustained drug delivery by a hierarchical nanostructured SiO2-CaO-P2O5 scaffold


Ramiro-Gutierrez, ML; Santos-Ruiz, L; Borrego-Gonzalez, S; Becerra, J; Diaz-Cuenca, A
Microporous and Mesoporous Materials, 229 (2016) 31-43

ABSTRACT

A hierarchical scaffold, SP1_h_HA, consisting of a biomimetic nano-hydroxyapatite surface coating growth onto a reticulated structure having a nano-organized porous texture was fabricated and functionally studied in vitro using osteoprogenitor cells. Three scaffold materials (designated as SP0_l, SP0_h and SP1_h) were also prepared through modifications of the processing variables as control materials. The scaffolds were characterized showing well-interconnected micron-sized voids and a nano (4–6 nm)-organized porosity. In order to evaluate potential local risks and performance over mammalian cells the scaffolds were studied in comparison with a commercial clinical grade scaffold material, ProOsteon® 500R. MC3T3-E1 pre-osteoblast viability was evaluated using the resazurin assay and field emission gun scanning electron microscopy (FEG-SEM), showing in all cases good proliferative response. Alkaline phosphatase (ALP) production and analysis of the differentiation marker osteocalcin (OC), both in non-osteoinductive and osteoinductive media, were assessed using colorimetric and RT-PCR methods. The implementation of the new scaffold processing variables enhanced ALP activity with respect to the SP0_l control material. The cell proliferation, ALP activity, and mRNA OC expression response to SP1_h_HA scaffold were higher than those observed after the use of ProOsteon® 500R. In addition, SP1_h_HA scaffold showed a two stage sustained release of gentamicin sulfate (GS) instead of the quick release shown by ProOsteon® 500R. These results suggest that our synthesized scaffold could be effective for antibiotic delivery and bone regeneration and a better option than ProOsteon® 500R.


Julio, 2016 | DOI: 10.1016/j.micromeso.2016.04.018

A Full Vacuum Approach for the Fabrication of Hybrid White-Light-Emitting Thin Films and Wide-Range In Situ Tunable Luminescent Microcavities


Y. Oulad-Zian, J.R. Sánchez-Valencia, M. Oliva, J. Parra-Barranco, M. Alcaire, F.J. Aparicio, A. Mora-Boza, J.P. Espinós, F. Yubero, A.R. González-Elipe, A. Barranco, A. Borras
Advanced Optical Materials, 4 (2016) 1134

ABSTRACT

A wide-range in situ tunable 1D Bragg microcavity including a hybrid layer as white light emitter defect is shown by J. R. Sanchez-Valencia, A. Borras, and co-workers on page 1124. White emission is obtained by Förster resonance energy transfer between blue (1,3,5-triphenyl-2-pyrazoline) and orange (rubrene) dyes homogeneously infiltrated within the host nanocolumnar SiO2film, which is formed by glancing angle deposition. Sequential physical vapor deposition at low temperatures provides the organic dyes localization within the porous nanostructure of the defect layer.


Junio, 2016 | DOI: 10.1002/adom.201670041

Dye-based photonic sensing systems


Aparicio, FJ; Alcaire, M; Gonzalez-Elipe, AR; Barranco, A; Holgado, M; Casquel, R; Sanza, FJ; Griol, A; Bernier, D; Dortu, F; Caceres, S; Antelius, M; Lapisa, M; Sohlstrom, H; Niklaus, F
Sensors and Actuators B: Chemical, 228 (2016) 649-657

ABSTRACT

We report on dye-based photonic sensing systems which are fabricated and packaged at wafer scale. For the first time luminescent organic nanocomposite thin-films deposited by plasma technology are integrated in photonic sensing systems as active sensing elements. The realized dye-based photonic sensors include an environmental NO2 sensor and a sunlight ultraviolet light (UV) A+B sensor. The luminescent signal from the nanocomposite thin-films responds to changes in the environment and is selectively filtered by a photonic structure consisting of a Fabry-Perot cavity. The sensors are fabricated and packaged at wafer-scale, which makes the technology viable for volume manufacturing. Prototype photonic sensor systems have been tested in real-world scenarios. 


Junio, 2016 | DOI: 10.1016/j.snb.2016.01.092

Portable IR dye laser optofluidic microresonator as a temperature and chemical sensor


Lahoz, F; Martin, IR; Gil-Rostra, J; Oliva-Ramirez, M; Yubero, F; Gonzalez-Elipe, AR
Optics Express, 24 (2016) 14383-14392

ABSTRACT

A compact and portable optofluidic microresonator has been fabricated and characterized. It is based on a Fabry-Perot microcavity consisting essentially of two tailored dichroic Bragg mirrors prepared by reactive magnetron sputtering deposition. The microresonator has been filled with an ethanol solution of Nile-Blue dye. Infrared laser emission has been measured with a pump threshold as low as 0.12 MW/cm2 and an external energy conversion efficiency of 41%. The application of the device as a temperature and a chemical sensor is demonstrated. Small temperature variations as well as small amount of water concentrations in the liquid laser medium are detected as a shift of the resonant laser modes.


Junio, 2016 | DOI: 10.1364/OE.24.014383

The 16th European Conference on Applications of Surface and Interface Analysis


Yubero, F
Surface and Interface Analysis

ABSTRACT

Non-enzymatic Glucose electrochemical sensor made of porous NiO thin films prepared by reactive magnetron sputtering at oblique angles


Garcia-Garcia, FJ; Salazar, P; Yubero, F; Gonzalez-Elipe, AR
Electrochimica Acta, 201 (2016) 38-44

ABSTRACT

Porous nanostructured NiO thin films have been prepared in one step by magnetron sputtering in an oblique angle configuration (MS-OAD) and used as electrodes for the non-enzymatic detection of glucose. The films have been thoroughly characterized by different complementary techniques and their performance for the analysis of glucose in basic solutions determined by electrochemical methods. These electrodes presented four times higher sensitivity that equivalent compact thin films prepared by MS in a normal configuration and were superior in terms of sensitivity than majority of nickel based electrodes prepared by other methods. Finally, a high sensitivity towards detection of glucose in blood, insensitivity to common interferences, a long term stability and high reproducibility confirmed the good performance and reliability of these electrodes for practical analytical purposes.


Mayo, 2016 | DOI: 10.1016/j.electacta.2016.03.193

The interaction between hybrid organic-inorganic halide perovskite and selective contacts in perovskite solar cells: an infrared spectroscopy study


Idigoras, J; Todinova, A; Sanchez-Valencia, JR; Barranco, A; Borras, A; Anta, JA
Physical Chemistry Chemical Physics, 18 (2016) 13583-13590

ABSTRACT

The interaction of hybrid organic-inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000-500 cm(-1)). The materials employed as substrates are not only characterized by different chemical natures (TiO2, ZnO and Al2O3), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N-H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid-base reaction that takes place through the NH3+ groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI2 formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO2, Al2O3, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.


Mayo, 2016 | DOI: 10.1039/c6cp01265e

Light management: porous 1-dimensional nanocolumnar structures as effective photonic crystals for perovskite solar cells


Ramos, FJ; Oliva-Ramirez, M; Nazeeruddin, MK; Graetzel, M; Gonzalez-Elipe, AR; Ahmad, S
Journal of Materials Chemistry A, 4 (2016) 4962-4970

ABSTRACT

Hybrid organic-inorganic perovskite solar cells are a topic of increasing interest, as in a short time span they are able to lead in the third generation photovoltaics. Organohalide perovskites possess exceptional optoelectronic and physical properties, thus making their implementation possible in many diverse configurations of photovoltaic devices. In this work, we present three different configurations of porous 1-dimensional photonic crystals (1-DPCs) based on alternated nanocolumnar layers of oxides with different refractive indices (n) that were deposited by Physical Vapor Deposition at Oblique Angle Deposition (PVD-OAD). They are then implemented as the photoanode in CH3NH3PbI3 solar cells to improve the management of light into the device. These configurations improved the performance of the photovoltaic system by designing a light interference structure capable of enhancing the absorption capability of the perovskite. A device fabricated using these photonic crystal structures presented an efficiency >12% in contrast with only 10.22% for a reference device based on non-photonic crystal TiO2 layers deposited under analogous conditions.


Abril, 2016 | DOI: 10.1039/c5ta08743k

Growth Assisted by Glancing Angle Deposition: A New Technique to Fabricate Highly Porous Anisotropic Thin Films


Sanchez-Valencia, JR; Longtin, R; Rossell, MD; Groning, P
ACS Applied Materials & Interfaces, 8 (2016) 8686-8693

ABSTRACT

We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a “proof of concept”, we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.


Abril, 2016 | DOI: 10.1021/acsami.6b00232

Nickel-copper bilayer nanoporous electrode prepared by physical vapor deposition at oblique angles for the non-enzymatic determination of glucose


Salazar, P; Rico, V; Gonzalez-Elipe, AR
Sensors and Actuators B: Chemical, 226 (2016) 436-443

ABSTRACT

This work presents a novel bilayer Ni/Cu porous nanostructured film electrode prepared by physical vapor deposition (PVD) in an oblique angle configuration. Scanning electron microscopy (SEM) data revealed that the film, with an approximate thickness of 200 nm, is formed by tilted nanocolumns of around 50 nm of diameter and an inclination of 30° with respect to the surface normal. X ray photoelectron spectroscopy (XPS) data confirmed a bilayer configuration with Cu and Ni located at the top and bottom parts of the film, respectively. A porosity of ca. 45–35% as determined by Rutherford back scattering (RBS) offered a large exposed area and excellent diffusion properties that, combined with a very good catalytic activity, rendered these films excellent electrodes for the quantitative determination of glucose. Under optimized working conditions of detection these electrodes presented a high sensitivity of 2.53 A M−1 cm−2 (R2: 0.999), a limit of detection of 0.23 μM and a time response of ca. 2 s. The sensors did not show any loss of response during a period of 4 months. The selectivity of the sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, in all cases with excellent results. The feasibility of using of this sensor for practical applications was confirmed by successfully determining the glucose content in different commercial beverages.


Abril, 2016 | DOI: 10.1016/j.snb.2015.12.003

Pre-prosthetic use of poly(lactic-co-glycolic acid) membranes treated with oxygen plasma and TiO2 nanocomposite particles for guided bone regeneration processes


Castillo-Dali, G; Castillo-Oyague, R; Terriza, A; Saffar, JL; Batista-Cruzado, A; Lynch, CD; Sloan, AJ; Gutierrez-Perez, JL; Torres-Lagares, D
Journal of Dentistry, 47 (2016) 71-79

ABSTRACT

Objectives: Guided bone regeneration (GBR) processes are frequently necessary to achieve appropriate substrates before the restoration of edentulous areas. This study aimed to evaluate the bone regeneration reliability of a new poly-lactic-co-glycolic acid (PLGA) membrane after treatment with oxygen plasma (PO2) and titanium dioxide (TiO2) composite nanoparticles. 

Methods: Circumferential bone defects (diameter: 10 mm; depth: 3 mm) were created on the parietal bones of eight experimentation rabbits and were randomly covered with control membranes (Group 1: PLGA) or experimental membranes (Group 2: PLGA/PO2/TiO2). The animals were euthanized two months afterwards, and a morphologic study was then performed under microscope using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone formed in the grown defects, concentration of osteoclasts, and intensity of osteosynthetic activity were assessed. Comparisons among the groups and with the original bone tissue were made using the Kruskal-Wallis test. The level of significance was set in advance at a = 0.05. 

Results: The experimental group recorded higher values for new bone formation, mineralised bone length, and osteoclast concentration; this group also registered the highest osteosynthetic activity. Bone layers in advanced formation stages and low proportions of immature tissue were observed in the study group. 


Abril, 2016 | DOI: 10.1016/j.jdent.2016.01.015

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation


Maddi, C; Bourquard, F; Tite, T; Loir, AS; Donnet, C; Garrelie, F; Barnier, V; Wolski, K; Fortgang, P; Zehani, N; Braiek, M; Lagarde, F; Chaix, C; Jaffrezic-Renault, N; Rojas, TC; Sanchez-Lopez, JC
Diamond and Related Materials,65 (2016) 17-25

ABSTRACT

Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to -350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at%. Nitrogen content increase induces a higher sp(2) character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor. 


Abril, 2016 | DOI: 10.1016/j.diamond.2016.01.001

Perspectives on oblique angle deposition of thin films: From fundamentals to devices


Barranco, A; Borras, A; Gonzalez-Elipe, AR; Palmero, A
Progress in Materials Science, 78 (2016) 59-153

ABSTRACT

The oblique angle configuration has emerged as an invaluable tool for the deposition of nanostructured thin films. This review develops an up to date description of its principles, including the atomistic mechanisms governing film growth and nanostructuration possibilities, as well as a comprehensive description of the applications benefiting from its incorporation in actual devices. In contrast with other reviews on the subject, the electron beam assisted evaporation technique is analyzed along with other methods operating at oblique angles, including, among others, magnetron sputtering and pulsed laser or ion beam-assisted deposition techniques. To account for the existing differences between deposition in vacuum or in the presence of a plasma, mechanistic simulations are critically revised, discussing well-established paradigms such as the tangent or cosine rules, and proposing new models that explain the growth of tilted porous nanostructures. In the second part, we present an extensive description of applications wherein oblique-angle-deposited thin films are of relevance. From there, we proceed by considering the requirements of a large number of functional devices in which these films are currently being utilized (e.g., solar cells, Li batteries, electrochromic glasses, biomaterials, sensors, etc.), and subsequently describe how and why these nanostructured materials meet with these needs. 


Marzo, 2016 | DOI: 10.1016/j.pmatsci.2015.06.003

Electrocatalytic System for the Simultaneous Hydrogen Production and Storage from Methanol


Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A
ACS Catalysis, 6 (2016) 1942-1951

ABSTRACT

This paper reports a groundbreaking approach for simultaneous hydrogen production and storage that entails catalysis, electrochemistry, surface science, and materials synthesis. A novel electrocatalytic system is developed based on nickel nanocolumnar films of controlled microstructure prepared on K-βAl2O3 solid electrolyte supports by oblique angle physical vapor deposition. The outstanding characteristics of this system are a hydrogen storage capacity of up to 19 g of H2 (100 g of Ni)−1, which is unparalleled in the literature and the possibility of controlling its release electrochemically, under fixed mild conditions (280 °C and normal pressure). H2 is produced in situ by methanol steam re-forming on the Ni catalyst, and it spills over onto graphene oxide aggregates formed during the catalytic process, as confirmed by SEM, FTIR, and Raman spectroscopy. The proposed storage mechanism considers a synergetic contribution of both Ni and graphene oxide, promoted by K+ ions, in enhancing the hydrogen storage capacity of the system.


Marzo, 2016 | DOI: 10.1021/acscatal.5b02844

Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique angles


Salazar, P; Garcia-Garcia, FJ; Yubero, F; Gil-Rostra, J; Gonzalez-Elipe, AR
Electrochimica Acta, 193 (2016) 24-31

ABSTRACT

In this communication we report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto indium tin oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behaviour, i.e. a linear working range from pH 1 to 12 with a slope of about -57.7 mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 months. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal reference electrode. This full solid state pH sensor presented a Nernstian behaviour with a slope of about -59 mV/pH and offered important analytical and operation advantages for decentralized pH measurements in different applications. 


Marzo, 2016 | DOI: 10.1016/j.electacta.2016.02.040

Nitrogen Nanobubbles in a-SiOxNy Coatings: Evaluation of Its Physical Properties and Chemical Bonding State by Spatially Resolved Electron Energy-Loss Spectroscopy


Lacroix, B.; Godinho, V.; Fernández, A.
Journal of Physical Chemistry C, 120 (2016) 5651-5658

ABSTRACT

Nanoporous silicon-based materials with closed porosity filled with the sputtering gas have been recently developed by magnetron sputtering. In this work the physical properties (density and pressure) of molecular nitrogen inside closed pores in a SiOxNy coating are investigated for the first time using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope. The paper offers a detailed methodology to record and process multiple EELS spectrum images (SIs) acquired at different energy ranges and with different dwell times. An adequate extraction and quantification of the N–K edge contribution due to the molecular nitrogen inside nanopores is demonstrated. Core-loss intensity and N chemical bond state were evaluated to retrieve 2D maps revealing the stable high density of molecular nitrogen (from 40 to 70 at./nm3) in nanopores of different size (20–11 nm). This work provides new insights into the quantification of molecular N2 trapped in porous nitride matrices that could also be applied to other systems.


Marzo, 2016 | DOI: 10.1021/acs.jpcc.5b09036

Determination of the Anisotropic Elastic Properties of Rocksalt Ge2Sb2Te5 by XRD, Residual Stress, and DFT


Cecchini, R; Kohary, K; Fernandez, A; Cabibbo, M; Marmier, A
Journal of Physical Chemistry C, 120 (2016) 5624-5629

ABSTRACT

The chalcogenide material Ge2Sb2Te5 is the prototype phase-change material, with widespread applications for optical media and random access memory. However, the full set of its independent elastic properties has not yet been published. In this study, we determine the elastic constants of the rocksalt Ge2Sb2Te5, experimentally by X-ray diffraction (XRD) and residual stress and computationally by density functional theory (DFT). The stiffnesses (XRD-stress/DFT) in GPa are C-11 = 41/58, C-12 = 7/8, and C-44 = 8/12, and the Zener ratio is 0.46/0.48. These values are important to understand the effect of elastic distortions and nonmelting processes on the performances of increasingly small phase change data bits.


Febrero, 2016 | DOI: 10.1021/acs.jpcc.5b09867

Vacuum template synthesis of multifunctional nanotubes with tailored nanostructured walls


Filippin, AN; Macias-Montero, M; Saghi, Z; Idigoras, J; Burdet, P; Barranco, A; Midgley, P; Anta, JA; Borras, A
Scientific Reports, 5 (2016) 20637

ABSTRACT

A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a post-annealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensor.


Febrero, 2016 | DOI: 10.1038/srep20637

Ripening and recrystallization of NaCl nanocrystals in humid conditions


Oliva-Ramirez, M; Macias-Montero, M; Borras, A; Gonzalez-Elipe, AR
RSC Advances, 6 (2016) 3778-3782

ABSTRACT

This study shows that Ostwald ripening, a universal mechanism responsible for the increase of crystal size during precipitation from solutions, can be meditated by ion diffusion through condensed monolayers of water that connect separated nanocrystals. In an environmental electron microscope we have observed "in situ" the time evolution of the number, shape, size and crystallographic texture of NaCl nanoparticles deposited by electron beam evaporation at oblique angles. Analysis of NaCl nanoparticles before and after water vapor condensation has evidenced that the size of nanocrystals is not the unique driving force inducing nanoparticle ripening and recrystallization, but the faceting of their crystalline habits and the amorphisation degree of the initially deposited nuclei also play important roles. These findings have implications for other crystallization and nucleation processes and can be of relevance for rock weathering and related phenomena.


Febrero, 2016 | DOI: 10.1039/C5RA22425J

Nanostructured Ti thin films by magnetron sputtering at oblique angles


Alvarez, R; Garcia-Martin, JM; Garcia-Valenzuela, A; Macias-Montero, M; Ferrer, FJ; Santiso, J; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Physics D-Applied Physics, 49 (2016) 045303

ABSTRACT

The growth of Ti thin films by the magnetron sputtering technique at oblique angles and at room temperature is analysed from both experimental and theoretical points of view. Unlike other materials deposited in similar conditions, the nanostructure development of the Ti layers exhibits an anomalous behaviour when varying both the angle of incidence of the deposition flux and the deposition pressure. At low pressures, a sharp transition from compact to isolated, vertically aligned, nanocolumns is obtained when the angle of incidence surpasses a critical threshold. Remarkably, this transition also occurs when solely increasing the deposition pressure under certain conditions. By the characterization of the Ti layers, the realization of fundamental experiments and the use of a simple growth model, we demonstrate that surface mobilization processes associated to a highly directed momentum distribution and the relatively high kinetic energy of sputtered atoms are responsible for this behaviour.


Febrero, 2016 | DOI: 10.1088/0022-3727/49/4/045303

Nanoindentation and scratch resistance of multilayered TiO2-SiO2 coatings with different nanocolumnar structures deposited by PV-OAD


Roa, JJ; Rico, V; Oliva-Ramirez, M; Gonzalez-Elipe, AR; Jimenez-Pique, E
Journal of Physics D-Applied Physics, 49 (2016) 13

ABSTRACT

This paper presents a study of the mechanical properties and an evaluation of damage mechanisms of nanocolumnar TiO2-SiO2 multilayer coatings prepared by physical vapour oblique angle deposition at different configurations (slanted, zigzag or chiral) and two zenithal evaporation angles (70 degrees or 85 degrees). The characterization at micro-and nanometric length scales of the mechanical properties of the multilayers has been carried out by nanoindentation and nanoscratch tests, while the morphological evaluation of the surface and sub-surface damages produced with a sharp indenter and the adhesive and/or cohesive failures between coating and substrate have been investigated by field emission scanning electron microscopy and focused ion beam, respectively. The obtained results have shown that the main processing parameters controlling the mechanical response of the different multilayers is the zenithal angle of deposition and the number of layers in the multilayer stack, while the coating architecture had only a minor effect on the mechanical response. This analysis also revealed a higher resistance to scratch testing and a brittle failure behaviour for the low zenithal angle coatings as compared with the high angle ones.


Febrero, 2016 | DOI: 10.1088/0022-3727/49/13/135104

Optofluidic Modulation of Self-Associated Nanostructural Units Forming Planar Bragg Microcavities


Oliva-Ramirez, M; Barranco, A; Loffler, M; Yubero, F; Gonzalez-Elipe, AR
ACS Nano, 10 (2016) 1256-1264

ABSTRACT

Bragg microcavities (BMs) formed by the successive stacking of nanocolumnar porous SiO2 and TiO2 layers with slanted, zigzag, chiral, and vertical configurations are prepared by physical vapor deposition at oblique angles while azimuthally varying the substrate orientation during the multilayer growth. The slanted and zigzag BMs act as wavelength-selective optical retarders when they are illuminated with linearly polarized light, while no polarization dependence is observed for the chiral and vertical cavities. This distinct optical behavior is attributed to a self-nanostructuration mechanism involving a fence-bundling association of nanocolumns as observed by focused ion beam scanning electron microscopy in the slanted and zigzag microcavities. The outstanding retarder response of the optically active BMs can be effectively modulated by dynamic infiltration of nano- and mesopores with liquids of different refraction indices acting as a switch of the polarization behavior. The unprecedented polarization and tunable optofluidic properties of these nanostructured photonic systems have been successfully simulated with a simple model that assumes a certain birefringence for the individual stacked layers and accounts for the light interference phenomena developed in the BMs. The possibilities of this type of self-arranged nanostructured and optically active BMs for liquid sensing and monitoring applications are discussed.


Enero, 2016 | DOI: 10.1021/acsnano.5b06625

Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications


Fernandez, A; Arzac, GM; Vogt, UF; Hosoglu, F; Borgschulte, A; de Haro, MCJ; Montes, O; Zuttel, A
Applied Catalysis B: Environmental, 180 (2016) 336-343

ABSTRACT

A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20 nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5 Lhydrogen min−1 gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50(temperature for 50% conversion) of 34 °C was obtained. Activation energy measured in our conditions was 35 ± 1 kJ mol−1.


Enero, 2016 | DOI: 10.1016/j.apcatb.2015.06.040

Application of Prussian Blue electrodes for amperometric detection of free chlorine in water samples using Flow Injection Analysis


Salazar, P; Martin, M; Gonzalez-Mora, JL; Gonzalez-Elipe, AR
Talanta, 146 (2016) 410-416

ABSTRACT

The performance for free chlorine detection of surfactant-modified Prussian Blue screen printed carbon electrodes (SPCEs/PB-BZT) have been assessed by cyclic voltammetry and constant potential amperometry. The characterization of SPCEs/PB-BZT by X-ray photoemission, Raman and infrared spectroscopies confirmed the correct electrodeposition of the surfactant-modified PB film. These electrodes were incorporated in a Flow Injection device and the optimal working conditions determined as a function of experimental variables such as detection potential, electrolyte concentration or flow-rate. The sensor presented a linear response in the range 0–3 ppm free chlorine, with a sensitivity of 16.2 μA ppm−1 cm−2. The limit of detection (LOD) (S/N=3.3) and the limit of quantification (S/N=10) amounted to 8.25 and 24.6 ppb, respectively, adequate for controlling tap and drinking waters. To demonstrate the feasibility of using this free chlorine sensor for real applications possible interferences such as nitrate, nitrite and sulfate ions were successfully tested and discarded. Real free chlorine analysis was carried out in spiked tap water samples and commercial bleaches.


Enero, 2016 | DOI: 10.1016/j.talanta.2015.08.072

Highly Porous ZnO Thin Films and 1D Nanostructures by Remote Plasma Processing of Zn-Phthalocyanine


Alcaire, M; Filippin, AN; Macias-Montero, M; Sanchez-Valencia, JR; Rojas, TC; Mora-Boza, A; Lopez-Santos, C; Espinos, JP; Barranco, A; Borras, A
Plasma Processes and Polymers, 13 (2016) 287-297

ABSTRACT

In this paper the fabrication of highly porous 1D nanostructures by a vacuum and plasma etching combined protocol is presented. Zn-phthalocyanine (ZnPc) is utilized as a solid precursor to form the ZnO. First the ZnPc is sublimated in low argon pressure. Depending on the substrate temperature and microstructure, polycrystalline films or single crystal ZnPc nanowires are grown. These starting materials are then subjected to a remote plasma oxidizing treatment. Experimental parameters such as substrate position, plasma power, treatment duration, and substrate temperature determine the microstructure and properties of the final ZnO nanostructures. The article gathers an in depth study of the obtained porous nanostructured films following scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV-Vis transmittance, and fluorescence spectroscopies.


Enero, 2016 | DOI: 10.1002/ppap.201500133

A novel 3D absorption correction method for quantitative EDX-STEM tomography


Burdet, P; Saghi, Z; Filippin, AN; Borras, A; Midgley, PA
Ultramicroscopy, 160 (2016) 118-129

ABSTRACT

This paper presents a novel 3D method to correct for absorption in energy dispersive X-ray (EDX) microanalysis of heterogeneous samples of unknown structure and composition. By using STEM-based tomography coupled with EDX, an initial 3D reconstruction is used to extract the location of generated X-rays as well as the X-ray path through the sample to the surface. The absorption correction needed to retrieve the generated X-ray intensity is then calculated voxel-by-voxel estimating the different compositions encountered by the X-ray. The method is applied to a core/shell nanowire containing carbon and oxygen, two elements generating highly absorbed low energy X-rays. Absorption is shown to cause major reconstruction artefacts, in the form of an incomplete recovery of the oxide and an erroneous presence of carbon in the shell. By applying the correction method, these artefacts are greatly reduced. The accuracy of the method is assessed using reference X-ray lines with low absorption.


Enero, 2016 | DOI: 10.1016/j.ultramic.2015.09.012

Quantitative analysis of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix


Pauly, N; Yubero, F; Garcia-Garcia, FJ; Tougaard, S
Surface Science, 644 (2016) 46-52

ABSTRACT

In X-ray excited photoelectron emission (XPS), besides the initial excitation process, the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To make an accurate quantitative interpretation of features observed in XPS, these effects must be included in the theoretical description of the emitted photoelectron spectra. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that these three effects can be calculated by means of the QUEELS-XPS software (Quantitative analysis of Electron Energy Losses at Surfaces for XPS) in terms of effective energy-differential inelastic electron scattering cross-sections. The only input needed to calculate these cross-sections is the energy loss function of the media which is determined from analysis of Reflection Electron Energy Loss Spectra (REELS). The full XPS spectrum is then modeled by convoluting this energy loss cross-section with the primary excitation spectrum that accounts for all effects which are part of the initial photo-excitation process, i.e. lifetime broadening, spin-orbit coupling, and multiplet splitting. In this paper we apply the previously presented procedure to the study of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix (Ni:SiO2), samples being prepared by reactive magnetron sputtering at room temperature. We observe a significant difference between the corresponding Ni 2p primary excitation spectra. The procedure allows quantifying the relative intensity of the c3d(9)L, c3d(10)L(2), and c3d(8) final states contributing to the Ni 2p photoemission spectra of the Ni2+ species in the oxide matrices. Especially, the intensity ratio in NiO between the non-local and local contributions to the 3d(9)L configuration is determined to be 2.5. Moreover the relative intensity ratio of the c3d(9)L/c3d(10)L(2)/c3d(8) configurations is found to be 1.0/0.83/0.11 for both the NiO and Ni:SiO2 samples. 


Enero, 2016 | DOI: 10.1016/j.susc.2015.09.012

Disorder-order phase transformation in a fluorite-related oxide thin film: In-situ X-ray diffraction and modelling of the residual stress effects


Gaboriaud, RJ; Paumier, F; Lacroix, B
Thin Solid Films, 601 (2016) 84-88

ABSTRACT

This work is focused on the transformation of the disordered fluorite cubic-F phase to the ordered cubic-C bixbyite phase, induced by isothermal annealing as a function of the residual stresses resulting from different concentrations of microstructural defects in the yttrium oxide, Y2O3. 

This transformation was studied using in-situ X-ray diffraction and was modelled using Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. The degree of the disorder of the oxygen network was associated with the residual stress, which was a key parameter for the stability and the kinetics of the transition of the different phases that were present in the thin oxide film. When the degree of disorder/residual stress level is high, this transition, which occurs at a rather low temperature (300 degrees C), is interpreted as a transformation of phases that occurs by a complete recrystallization via the nucleation and growth of a new cubic-C structure. Using the KJMA model, we determined the activation energy of the transformation process, which indicates that this transition occurs via a one-dimensional diffusion process. Thus, we present the analysis and modelling of the stress state. When the disorder/residual stress level was low, a transition to the quasi-perfect ordered cubic-C structure of the yttrium oxide appeared at a rather high temperature (800 degrees C), which is interpreted as a classic recovery mechanism of the cubic-C structure.


Enero, 2016 | DOI: 10.1016/j.tsf.2015.08.030



2015


Optical properties of zirconium oxynitride films: The effect of composition, electronic and crystalline structures


Carvalho, P; Borges, J; Rodrigues, MS; Barradas, NP; Alves, E; Espinos, JP; Gonzalez-Elipe, AR; Cunha, L; Marques, L; Vasilevskiy, MI; Vaz, F
Applied Surface Science, 358 (2015) 660-669

ABSTRACT

This work is devoted to the investigation of zirconium oxynitride (ZrOxNy) films with varied optical responses prompted by the variations in their compositional and structural properties. The films were prepared by dc reactive magnetron sputtering of Zr, using Ar and a reactive gas mixture of N-2 + O-2 ( 17:3). The colour of the films changed from metallic-like, very bright yellow-pale and golden yellow, for low gas flows to red-brownish for intermediate gas flows. Associated to this colour change there was a significant decrease of brightness. With further increase of the reactive gas flow, the colour of the samples changed from red-brownish to dark blue or even to interference colourations. The variations in composition disclosed the existence of four different zones, which were found to be closely related with the variations in the crystalline structure. XRD analysis revealed the change from a B1 NaCl face-centred cubic zirconium nitride-type phase for films prepared with low reactive gas flows, towards a poorly crystallized over-stoichiometric nitride phase, which may be similar to that of Zr3N4 with some probable oxygen inclusions within nitrogen positions, for films prepared with intermediate reactive gas flows. For high reactive gas flows, the films developed an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions, evolving to a ZrO2 monoclinic type structure within the zone where films were prepared with relatively high reactive gas flows. The analysis carried out by reflected electron energy loss spectroscopy (REELS) revealed a continuous depopulation of the d-band and an opening of an energy gap between the valence band (2p) and the Fermi level close to 5 eV. The ZrN-based coatings (zone land II) presented intrinsic colourations, with a decrease in brightness and a colour change from bright yellow to golden yellow, red brownish and dark blue. Associated to these changes, there was also a shift of the reflectivity minimum to lower energies, with the increase of the non-metallic content. The samples lying in the two last zones (zone III, oxynitride and zone IV, oxide films) revealed a typical semi-transparent-optical behaviour showing interference-like colourations only due to the complete depopulation of the d band at the Fermi level. The samples lying in these zones presented also an increase of the optical bandgap from 2 to 3.6 eV. 


Diciembre, 2015 | DOI: 10.1016/j.apsusc.2015.09.129

Efficient synthesis of ammonia from N-2 and H-2 alone in a ferroelectric packed-bed DBD reactor


Gomez-Ramirez, A; Cotrino, J; Lambert, RM; Gonzalez-Elipe, AR
Plasma Sources Science and Technology, 24 (2015) 065011

ABSTRACT

A detailed study of ammonia synthesis from hydrogen and nitrogen in a planar dielectric barrier discharge (DBD) reactor was carried out. Electrical parameters were systematically varied, including applied voltage and frequency, electrode gap, and type of ferroelectric material (BaTiO3 versus PZT). For selected operating conditions, power consumption and plasma electron density were estimated from Lissajous diagrams and by application of the Bolsig + model, respectively. Optical emission spectroscopy was used to follow the evolution of plasma species (NH*, N*, N-2(+) and N-2*) as a function of applied voltage with both types of ferroelectric material. PZT gave both greater energy efficiency and higher ammonia yield than BaTiO3: 0.9 g NH3 kWh(-1) and 2.7% single pass N-2 conversion, respectively. This performance is substantially superior to previously published findings on DBD synthesis of NH3 from N-2 and H-2 alone. The influence of electrical working parameters, the beneficial effect of PZT and the importance of controlling reactant residence time are rationalized in a reaction model that takes account of the principal process variables


Diciembre, 2015 | DOI: 10.1088/0963-0252/24/6/065011

Plasma reforming of methane in a tunable ferroelectric packed-bed dielectric barrier discharge reactor


Montoro-Damas, AM; Brey, JJ; Rodriguez, MA; Gonzalez-Elipe, AR; Cotrino, J
Journal of Power Sources, 296 (2015) 268-275

ABSTRACT

In a tunable circular parallel plate dielectric barrier discharge reactor with pellets of a ferroelectric material separating the electrodes we investigate the plasma reforming of methane trying to maximize both the reaction yield and the energetic efficiency of the process. The geometrical configuration of the reactor (gap between electrodes, active electrode area) and the ferroelectric pellet size have been systematically varied to determine their influence on the process efficiency. The comparison between wet (with H2O as reactant), oxidative (with O2), and dry (with CO2) reforming reactions reveals a higher efficiency for the former with CO + H2 as main reaction products. The maximum energetic efficiency EE, defined as the produced number of litres of H2 per kWh, found for optimized working conditions at low-level applied power is higher than the up to date best-known results. A comprehensive discussion of the influence of the different parameters affecting the reaction yield is carried out.


Noviembre, 2015 | DOI: 10.1016/j.jpowsour.2015.07.038

Single-step fabrication process of 1-D photonic crystals coupled to nanocolumnar TiO2 layers to improve DSC efficiency


Gonzalez-Garcia, L; Colodrero, S; Miguez, H; Gonzalez-Elipe, AR
Optics Express, 23 (2015) A1642-A1650

ABSTRACT

The present work proposes the use of a TiO2 electrode coupled to a one-dimensional photonic crystal (1DPC), all formed by the sequential deposition of nanocolumnar thin films by physical vapor oblique angle deposition (PV-OAD), to enhance the optical and electrical performance of DSCs while transparency is preserved. We demonstrate that this approach allows building an architecture combining a non-dispersive 3 µm of TiO2 electrode and 1 µm TiO2-SiO2 1DPC, both columnar, in a single-step process. The incorporation of the photonic structure is responsible for a rise of 30% in photovoltaic efficiency, as compared with a transparent cell with a single TiO2 electrode. Detailed analysis of the spectral dependence of the photocurrent demonstrates that the 1DPC improves light harvesting efficiency by both back reflection and optical cavity modes confinement within the TiO2 films, thus increasing the overall performance of the cell.


Noviembre, 2015 | DOI: 10.1364/OE.23.0A1642

Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices


Beltran, AM; Duguay, S; Strenger, C; Bauer, AJ; Cristiano, F; Schamm-Chardon, S
Solid State Communications, 221 (2015) 28-32

ABSTRACT

The breakthrough of 4H-SiC MOSFETs is stemmed mainly due to the mobility degradation in their channel in spite of the good physical intrinsic material properties. Here, two different n-channel 4H-SiC MOSFETs are characterized in order to analyze the elemental composition at the SiC/SiO2 interface and its relationship to their electrical properties. Elemental distribution analyses performed by EELS reveal the existence of a transition layer between the SiC and the SiO2 regions of the same width for both MOSFETs despite a factor of nearly two between their electron mobility. Additional 3D compositional mapping by atom probe tomography corroborates these results, particularly the absence of an anomalous carbon distribution around the SiC/SiO2interface.


Noviembre, 2015 | DOI: 10.1016/j.ssc.2015.08.017

Full solution processed mesostructured optical resonators integrating colloidal semiconductor quantum dots


Calvo, ME; Hidalgo, N; Schierholz, R; Kovacs, A; Fernandez, A; Bellino, MG; Soler-Illia, GJAA; Miguez, H
Nanoscale, 7 (2015) 16583-16589

ABSTRACT

Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure.


Octubre, 2015 | DOI: 10.1039/C5NR03977K

Role of Y in the oxidation resistance of CrAlYN coatings


Dominguez-Meister, S; El Mrabet, S; Escobar-Galindo, R; Mariscal, A; de Haro, CJ; Justo, A; Brizuela, M; Rojas, TC; Sanchez-Lopez, JC
Applied Surface Science, 363 (2015) 504-511

ABSTRACT

CrAlYN coatings with different aluminum (4–12 at.%) and yttrium (2–5 at.%) contents are deposited by d.c. reactive magnetron sputtering on silicon and M2 steel substrates using metallic targets and Ar/N2 mixtures. The influence of the nanostructure and chemical elemental distribution on the oxidation resistance after heating in air at 1000 °C is studied by means of cross-sectional scanning electron microscopy (X-SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GD-OES). The sequential exposure to the metallic targets during the synthesis leads to a multilayer structure where concentration of metallic elements (Cr, Al and Y) is changing periodically. A good oxidation resistance is observed when Al- and Y-rich regions are separated by well-defined CrN layers, maintaining crystalline coherence along the columnar structure. This protective behavior is independent of the type of substrate and corresponds to the formation of a thin mixed (Al, Cr)-oxide scale that protects the film underneath. The GD-OES and XRD analysis have demonstrated that Y acts as a reactive element, blocking the Fe and C atoms diffusion from the steel and favoring higher Al/Cr ratio in the passivation layer after heating. The coating with Y content around 4 at.% exhibited the best performance with a thinner oxide scale, a delay in the CrN decomposition and transformation to Cr2N, and a more effective Fe and C blocking.


Octubre, 2015 | DOI: 10.1016/j.apsusc.2015.06.099

Amperometric magnetobiosensors using poly(dopamine)-modified Fe3O4 magnetic nanoparticles for the detection of phenolic compounds


Martin, M; Salazar, P; Campuzano, S; Villalonga, R; Pingarron, JM; Gonzalez-Mora, JL
Analytical Methods, 7 (2015) 8801-8808

ABSTRACT

The synthesis of poly(dopamine)-modified magnetic nanoparticles (MNPs) and their application in preparing electrochemical enzyme biosensors that are useful to detect phenolic compounds is reported in this work. MNPs of about 16 nm were synthesized by a co-precipitation method and conveniently modified with poly(dopamine). Non-modified and modified MNPs were characterized using X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). Horseradish peroxidase (HRP) was covalently immobilized onto the surface of the poly(dopamine)-modified MNPs via Michael addition and/or Schiff base formation and used to construct a biosensor for phenolic compounds by capturing the HRP-modified-nanoparticles onto the surface of a magnetic-modified glassy carbon electrode (GCE). Cyclic voltammetry and amperometry were used to study the electrochemical and analytical properties of the biosensor using hydroquinone (HQ) as a redox probe. Among the different phenolic compounds studied, the biosensor exhibited higher sensitivity for HQ, 1.38 A M−1 cm−2, with limits of detection and quantification of 0.3 and 1.86 μM, respectively. The analytical biosensor performance for HQ and 2-aminophenol compared advantageously with those of previous phenolic biosensors reported in the literature.


Octubre, 2015 | DOI: 10.1039/C5AY01996F

"In situ" XPS studies of laser-induced surface nitridation and oxidation of tantalum


Lahoz, R; Espinos, JP; Yubero, F; Gonzalez-Elipe, AR; de la Fuente, GF
Journal of Materials Research, 30 (2015) 2967-2976

ABSTRACT

This work studies the nitridation of Ta by laser irradiation by means of x-ray photoelectron spectroscopy. The study has been carried out under "in situ" conditions by controlling the nitrogen partial pressure, the presence of traces of oxygen, and the irradiance of the laser. It is found that a thin layer of Ta2O5 is directly obtained when irradiating in the presence of oxygen, while a Ta3N5 surface compound and some minor contributions of nonstoichiometric phases are formed in the presence of nitrogen. For O-2:N-2 mixtures at 0.1 Pa, preferential nitride formation occurs up to a ratio of 1:4, while Ta2O5 starts to be predominant for ratios above this value. The air stability of the tantalum nitride layer formed by laser irradiation and the surface topography of the irradiated metal are also studied. The possible factors determining this behavior are discussed.


Octubre, 2015 | DOI: 10.1557/jmr.2015.190

Physiological Degradation Mechanisms of PLGA Membrane Films under Oxygen Plasma Treatment


Lopez-Santos, C; Terriza, A; Portoles, J; Yubero, F; Gonzalez-Elipe, AR
Journal fo Physical Chemistry C, 119 (2015) 20446–20452

ABSTRACT

Degradation under simulated physiological conditions of poly(lactic-co-glycolic) (PLGA) copolymer membrane films subjected to an oxygen plasma treatment compared to its “as prepared” state has been studied by gas cluster ion beam assisted X-ray photoelectron spectroscopy for chemical depth profiling analysis. This investigation is complemented with atomic force microscopy, weight loss measurements, and visual inspection of the films at the different stages of the degradation process. The obtained results show that the carbon functional groups of the PLGA membrane films undergo a heterogeneous hydrolytic degradation to different rates depending on the plasma pretreatment. The content of glycolic groups (GA) in untreated PLGA samples immersed for 3 weeks in a phosphate-buffered saline solution decreased at the surface, whereas the ratio between glycolic and lactic units (LA) did not vary in the inner regions (∼400 nm depth) of the degraded membrane films. By contrast, oxygen plasma pretreatment enhances the degradation efficiency and causes that both lactic and glycolic functional components decreased at the surface and in the interior of the film, although with less prevalence for the lactic units that present a comparatively higher resistance to degradation.


Septiembre, 2015 | DOI: 10.1021/acs.jpcc.5b05011

Microstructure of mixed oxide thin films prepared by magnetron sputtering at oblique angles


Gil-Rostra, J; Garcia-Garcia, FJ; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F
Thin Solid Films, 591 (2015) 330-335

ABSTRACT

Several mixed oxide thin film series of samples (Si–Co–O, Si–Ni–O, Si–W–O) have been prepared by reactive magnetron sputtering at oblique angle geometries. The paper focuses on the description of microstructure of the films as a function of their stoichiometry. It is found that for identical process parameters (gas mixture, pressure, magnetron-substrate distance, incidence angle of the vapour flux, etc.) the tilt angle of the developed columnar microstructure and the film porosity is strongly dependent on the stoichiometry of the films. The results are discussed in the framework of several theoretical models on this topic.


Septiembre, 2015 | DOI: 10.1016/j.tsf.2015.01.058

Rapid Legionella pneumophila determination based on a disposable core–shell Fe3O4@poly(dopamine) magnetic nanoparticles immunoplatform


Martin, M; Salazar, P; Jimenez, C; Lecuona, M; Ramos, MJ; Ode, J; Alcoba, J; Roche, R; Villalonga, R; Campuzano, S; Pingarron, JM; Gonzalez-Mora, JL
Analytica Chimica Acta, 887 (2015) 51-58

ABSTRACT

A novel amperometric magnetoimmunoassay, based on the use of core–shell magnetic nanoparticles and screen-printed carbon electrodes, was developed for the selective determination of Legionella pneumophila SG1. A specific capture antibody (Ab) was linked to the poly(dopamine)–modified magnetic nanoparticles (MNPs@pDA-Ab) and incubated with bacteria. The captured bacteria were sandwiched using the antibody labeled with horseradish peroxidase (Ab-HRP), and the resulting MNPs@pDA-Ab-Legionella neumophila-Ab-HRP were captured by a magnetic field on the electrode surface. The amperometric response measured at −0.15 V vs. Ag pseudo-reference electrode of the SPCE after the addition of H2O2 in the presence of hydroquinone (HQ) was used as transduction signal. The achieved limit of detection, without pre-concentration or pre-enrichment steps, was 104 Colony Forming Units (CFUs) mL−1. The method showed a good selectivity and the MNPs@pDA-Ab exhibited a good stability during 30 days. The possibility of detecting L. pneumophila at 10 CFU mL−1 level in less than 3 h, after performing a membrane-based preconcentration step, was also demonstrated.


Agosto, 2015 | DOI: 10.1016/j.aca.2015.05.048

Ultraviolet Pretreatment of Titanium Dioxide and Tin-Doped Indium Oxide Surfaces as a Promoter of the Adsorption of Organic Molecules in Dry Deposition Processes: Light Patterning of Organic Nanowires


Oulad-Zian, Y; Sanchez-Valencia, JR; Parra-Barranco, J; Hamad, S; Espinos, JP; Barranco, A; Ferrer, J; Coll, M; Borras, A
Langmuir, 31 (2015) 8294-8302

ABSTRACT

In this article we present the preactivation of TiO2 and ITO by UV irradiation under ambient conditions as a tool to enhance the incorporation of organic molecules on these oxides by evaporation at low pressures. The deposition of p-stacked molecules on TiO2 and ITO at controlled substrate temperature and in the presence of Ar is thoroughly followed by SEM, UV-vis, XRD, RBS, and photoluminescence spectroscopy, and the effect is exploited for the patterning formation of small-molecule organic nanowires (ONWs). X-ray photoelectron spectroscopy (XPS) in situ experiments and molecular dynamics simulations add critical information to fully elucidate the mechanism behind the increase in the number of adsorption centers for the organic molecules. Finally, the formation of hybrid organic/inorganic semiconductors is also explored as a result of the controlled vacuum sublimation of organic molecules on the open thin film microstructure of mesoporous TiO2.


Agosto, 2015 | DOI: 10.1021/acs.langmuir.5b01572

Modulating Low Energy Ion Plasma Fluxes for the Growth of Nanoporous Thin Films


Alvarez, Rafael; Lopez-Santos, Carmen; Ferrer, Francisco J.; Rico, Victor; Cotrino, Jose; Gonzalez-Elipe, Agustin R.; Palmero, Alberto
Plasma Processes and Polymers, 12 (2015) 719-724

ABSTRACT

The growth of nanoporous layers by plasma-assisted deposition techniques is strongly mediated by the ion fluxes in the reactor. To analyze their influence we have deposited different nanostructured thin films by the magnetron sputtering technique at oblique angles, modulating the ion fluxes in the plasma by tuning the frequency of the electromagnetic signal from pure DC to 160 kHz DC pulsed mode. In the DC case, ions possess energies below 5 eV and do not induce noticeable changes in the film structure. However, when the signal is pulsed, ions with energies up to 40 eV impinge on the film, decreasing the porosity of the layers and tilting down the porous/nanocolumnar structures. As a result, we demonstrate that the overall porosity of the layers and the tilt angle of the columns can be tailored as two independent morphological quantities.


Agosto, 2015 | DOI: 10.1002/ppap.201400209

Direct observation of doping incorporation pathways in self-catalytic GaMnAs


Kasama, T.; Thuvander, M.; Siusys, A.; Gontard, L. C.; Kovacs, A.; Yazdi, S.; Duchamp, M.; Gustafsson, A.; Dunin-Borkowski, R. E.; Sadowski, J.
Journal of Applied Physics, 118 (2015) 054302

ABSTRACT

Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 °C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 ± 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process.


Agosto, 2015 | DOI: 10.1063/1.4927623

Nanocolumnar 1-dimensional TiO2 photoanodes deposited by PVD-OAD for perovskite solar cell fabrication


Javier Ramos, F.; Oliva-Ramirez, Manuel; Nazeeruddin, Mohammad Khaja; Graetzel, Michael; Gonzalez-Elipe, Agustin R.; Ahmad, Shahzada
Journal of Materials Chemistry A, 3 (2015) 13291-13298

ABSTRACT

Perovskite solar cells have attracted increasing interest among the photovoltaic community in the last few years owing to their unique properties and high efficiency. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional porous TiO2 photoanodes, which are uniform on a large area. These nanocolumnar porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration (PVD-OAD) by varying the zenithal angle between the target and the substrate normal. Perovskite infiltration into these 1-dimensional nanocolumnar structures was homogeneous through the entire thickness of the porous layer as revealed by secondary ion mass spectroscopy studies. The fabricated solar cells, with an optimized thickness of the photoanode and with industrially accepted methods, will pave the way for easy implementation on a large scale.


Julio, 2015 | DOI: 10.1039/c5ta02238j

Fabrication of Optical Multi layer Devices from Porous Silicon Coatings with Closed Porosity by Magnetron Sputtering


Caballero-Hernandez, Jaime; Godinho, Vanda; Lacroix, Bertrand; Jimenez de Haro, Maria C.; Jamon, Damien; Fernandez, Asuncion
ACS Applied Materials & Interfaces, 7 (2015) 13880-13897

ABSTRACT

The fabrication of single-material photonic-multilayer devices is explored using a new methodology to produce porous silicon layers by magnetron sputtering. Our bottom-up methodology produces highly stable amorphous porous silicon films with a controlled refractive index using magnetron sputtering and incorporating a large amount of deposition gas inside the closed pores. The influence of the substrate bias on the formation of the closed porosity was explored here for the first time when He was used as the deposition gas. We successfully simulated, designed, and characterized Bragg reflectors and an optical microcavity that integrates these porous layers. The sharp interfaces between the dense and porous layers combined with the adequate control of the refractive index and thickness allowed for excellent agreement between the simulation and the experiments. The versatility of the magnetron sputtering technique allowed for the preparation of these structures for a wide range of substrates such as polymers while also taking advantage of the oblique angle deposition to prepare Bragg reflectors with a controlled lateral gradient in the stop band wavelengths.


Julio, 2015 | DOI: 10.1021/acsami.5b02356

New Copper wide range nanosensor electrode prepared by physical vapor deposition at oblique angles for the non-enzimatic determination of glucose


Salazar, P; Rico, V; Rodriguez-Amaro, R; Espinos, JP; Gonzalez-Elipe, AR
Electrochimica Acta, 169 (2015) 195-201

ABSTRACT

In this work a novel Cu nanostructured electrode is presented. Cu tilted nanocolumnar and porous thin films have been prepared by physical vapor deposition (PVD) in an oblique angle configuration and characterized by different techniques. Cyclic voltammetry and amperometry were used to study the sensing ability of the copper films deposited on ITO to quantitatively determine glucose and to optimize the experimental conditions of detection. Scanning electron microscopy data revealed that the film microstructure consists of tilted nanocolumns of around 70 nm of diameter and an inclination of 65° with respect to the surface normal that extend through the total thickness of the layer of ca. 300 nm. X ray photoelectron spectroscopy and Raman, used to determine the oxidation state of Cu, revealed that an oxy/hydroxide external layer formed around the nanocolumns is the active phase responsible for the electrocatalytic detection of glucose. Under optimized conditions, the CuO/Cu nanoporous/ITO electrode presented a sensitivity of 1.41 A mol dm−3 cm−2 (R2:0.999) with a limit of detection of 0.36 μmol dm−3 and a reproducibility of 3.42%.The selectivity of the proposed sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, thereby showing excellent anti-interference properties. The CuO/Cu nanoporous/ITO electrode was also used successfully to determine glucose in blood samples showing a performance comparable to that of a commercial glucometer. An extended working range covering from 1 to 5 × 10−3 mol dm−3 was determined for these sensor films which, in this way, could be applied for different analytical purposes including agro industrial liquids.


Julio, 2015 | DOI: 10.1016/j.electacta.2015.04.092

A novel and improved surfactant-modified Prussian Blue electrode for amperometric detection of free chlorine in water


Salazar, Pedro; Martin, Miriam; Garcia-Garcia, Francisco J.; Luis Gonzalez-Mora, Jose; Gonzalez-Elipe, Agustin R.
Sensors and Actuators B: Chemical, 213 (2015) 116-123

ABSTRACT

A surfactant-modified Prussian Blue (PB) electrochemical sensor has been developed. Benzethonium was used to assist the electrodeposition of PB onto a glassy carbon electrode (GCE). The surface coverage ( [View the MathML source] ) was 7.75 × 10−8 mol cm−2, five times higher than the value obtained in the absence of surfactant, and the film thickness of ca. 123 nm. SEM, EDX, Raman were used to characterize the electrodes while their electrochemical analysis proved a superior performance for the surfactant modified PB film. Cyclic voltammetry and amperometry were used to study the sensor ability to detect chlorine, and the main experimental variables were optimized. Under optimized conditions, the sensor presented a sensitivity of 12 μA ppm−1 cm−2, a linear range from 9 ppb to 10 ppm and a reproducibility of 4.2%. For the first time, we proved the sensor performance for real applications. Thus, chlorine was determined in tap water and the obtained concentrations validated with a standard colorimetric method. The obtained results showed that our sensor is highly performant and reliable for applications involving determinations of environmental residual chlorine.


Julio, 2015 | DOI: 10.1016/j.snb.2015.02.092

Removing the effects of the "dark matter" in tomography


Gontard, Lionel C.
Ultramicroscopy, 154 (2015) 64-72

ABSTRACT

Electron tomography (ET) using different imaging modes has been progressively consolidating its position as a key tool in materials science. The fidelity of a tomographic reconstruction, or tomogram, is affected by several experimental factors. Most often, an unrealistic cloud of intensity that does not correspond to a real material phase of the specimen ("dark matter") blurs the tomograms and enhances artefacts arising from the missing wedge (MW). Here we show that by simple preprocessing of the background level of any tomographic tilt series, it is possible to minimise the negative effects of that "dark matter". Iterative reconstruction algorithms converge better, leading to tomograms with fewer streaking artefacts from the MW, more contrast, and increased accuracy. The conclusions are valid irrespective of the imaging mode used, and the methodology improves the segmentation and visualisation of tomograms of both crystalline and amorphous materials. We show examples of HAADF STEM and BF TEM tomography.


Julio, 2015 | DOI: 10.1016/j.ultramic.2015.03.017

Core-shell polydopamine magnetic nanoparticles as sorbent in micro-dispersive solid-phase extraction for the determination of estrogenic compounds in water samples prior to high-performance liquid chromatography-mass spectrometry analysis


Socas-Rodriguez, B; Hernandez-Borges, J; Salazar, P; Martin, M; Rodriguez-Delgado, MA
Journal of Chromatography A, 1397 (2015) 1-10

ABSTRACT

In this work, core-shell Fe3O4@poly(dopamine) magnetic nanoparticles (m-NPs) were prepared and characterized in our laboratory and applied as sorbents for the magnetic-micro solid phase extraction (m-mu SPE) of twelve estrogenic compounds of interest (i.e. 17 alpha-estradiol, 17 beta-estradiol, estrone, hexestrol, 17 alpha-ethynylestradiol, diethylstibestrol, dienestrol, zearalenone, alpha-zearalanol,beta-zearalanol, alpha-zearalenol and beta-zearalenol) from different water samples. Separation, determination and quantification were achieved by high-performance liquid chromatography coupled to ion trap mass spectrometry with electrospray ionization. NPs@poly(dopamine) were synthesized by a chemical coprecipitation procedure and characterized by different surface characterization techniques (X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, infrared and Raman spectroscopy, vibrating sample magnetometry, microelectrophoresis and adsorption/desorption isotherms). Parameters affecting the extraction efficiency of m-mu SPE (i.e. polymerization time, pH of the sample, extraction and elution conditions) were studied and optimized. The methodology was validated for Milli-Q, mineral, tap and wastewater using 2-methoxyestradiol as internal standard, obtaining recoveries ranging from 70 to 119% with relative standard deviation values lower than 20% and limits of quantification in the range 0.02-1.1 mu g/L.


Junio, 2015 | DOI: 10.1016/j.chroma.2015.04.010

Island-type growth of Au–Pt heterodimers: direct visualization of misfit dislocations and strain-relief mechanisms


Garcia-Negrete, CA; Knappett, BR; Schmidt, FP; Rojas, TC; Wheatley, AEH; Hofer, F; Fernandez, A
RSC Advances, 5 (2015) 55262-55268

ABSTRACT

Structural and analytical characterization related to the formation mechanism of Au–Pt heterodimers from polyhedral Pt nanocrystals is reported. The observation of specific lattice strain effects and the emergence of misfit dislocations point to the relevance of the Stranski–Krastanov growth mode as a means of explaining the previously reported dimerisation reaction between Au and Pt. Two size-dependent strain relief mechanisms were identified. For dimers grown from 4.7 nm seeds, the mechanism is related to bulk lattice strain accumulation at {111} planes along with lattice relaxation effects on other crystalline planes. However, for dimers grown from 11.2 nm seed sizes, the formation of misfit dislocations proved to be a highly efficient mechanism by which to release interface mismatch strain. Nanoscale chemical mapping at Au–Pt interfaces also revealed Au–Pt alloying to be unlikely under the mild temperature conditions employed in this work for Au–Pt heterodimer synthesis.


Junio, 2015 | DOI: 10.1039/C5RA09808D

Porous, robust highly conducting Ni-YSZ thin film anodes prepared by magnetron sputtering at oblique angles for application as anodes and buffer layers in solid oxide fuel cells


Garcia-Garcia, Francisco J.; Yubero, Francisco; Gonzalez-Elipe, Agustin R.; Balomenou, Stella P.; Tsiplakides, Dimitris; Petrakopoulou, Ioanna; Lambert, Richard M.
Inernational Journal of Hydrogen Energy, 40 (2015) 7382-7387

ABSTRACT

Uniform, highly porous, columnar thin films incorporating YSZ and NiO prepared by magnetron sputtering with deposition at glancing incidence exhibited stoichiometries close to that of the Y-Zr-Ni sputter target. Characterization by means of SEM, XRD, XPS and RBS revealed that the uniformly distributed nickel component in the as-deposited films consisted of NiO, and that the YSZ component was essentially amorphous. Annealing such films at 850 degrees C in hydrogen resulted in crystallization of the YSZ phase with preservation of the columnar morphology, while the NiO underwent reduction to metallic Ni, which partially segregated to the film surface. The hydrogen-annealed thin film anodes exhibited high conductivity, comparable to that of conventionally-prepared anodes, in both hydrogen and hydrogen/water mixtures at temperatures relevant to SOFC operation. They were also robust against strain-induced separation from the substrate under limited thermal cycling in both oxidizing and reducing atmospheres and are promising candidates for use as anodes in their own right and as strain-accommodating buffer layers between conventional anodes and the electrolyte for use in SOFC applications.


Junio, 2015 | DOI: 10.1016/j.ijhydene.2015.04.001

Theory and Practice: Bulk Synthesis of C3B and its H2- and Li-Storage Capacity


King, TC; Matthews, PD; Glass, H; Cormack, JA; Holgado, JP; Leskes, M; Griffin, JM; Scherman, OA; Barker, PD; Grey, CP; Dutton, SE; Lambert, RM; Tustin, G; Alavi, A; Wright, DS
Angewandte Chemie International Edition, 54 (2015) 5919-5923

ABSTRACT

Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2- and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in a new generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2- and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered.


Mayo, 2015 | DOI: 10.1002/anie.201412200

Anisotropic In-Plane Conductivity and Dichroic Gold Plasmon Resonance in Plasma-Assisted ITO Thin Films e-Beam-Evaporated at Oblique Angles


Parra-Barranco, Julian; Garcia-Garcia, Francisco J.; Rico, Victor; Borras, Ana; Lopez-Santos, Carmen; Frutos, Fabian; Barranco, Angel; Gonzalez-Elipe, Agustin R.
ACS Applied Materials & Interfaces, 7 (2015) 10993-11001

ABSTRACT

ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy, and glancing incidence small-angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma-assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or the perpendicular to it. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light.


Mayo, 2015 | DOI: 10.1021/acsami.5b02197

Electrochemical activation of an oblique angle deposited Cu catalyst film for H-2 production


Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A
Catalysis Science & Technology, 5 (2015) 2203-2214

ABSTRACT

A novel Cu catalyst film was prepared by oblique angle physical vapour deposition (OAD) on a K-βAl2O3 solid electrolyte (alkaline ionic conductor) for catalytic/electrocatalytic purposes. This technique allowed us to obtain a highly porous and electrically conductive Cu catalyst electrode which was tested in the partial oxidation of methanol (POM) reaction for H2 production and its catalytic activity was in situ enhanced via electrochemical promotion of catalysis (EPOC). The electropromotional effect was reversible and reproducible, and allowed us to increase both hydrogen and methyl formate production rates by almost three times under optimal promotion conditions (320 °C, 2.2 × 10−7 mol of K+ transferred). The observed promotional effect was attributed to a decrease in the Cu catalyst work function as a consequence of the controlled migration of electropositive K+ ions which favoured the chemisorption of electron acceptor molecules (O2) at the expense of the electron donor ones (CH3OH). Under the reaction conditions these ions formed some kinds of potassium surface compounds as demonstrated by SEM, EDX and XPS post-reaction characterization analyses. The obtained results demonstrate the interest of the used catalyst-electrode preparation technique for the electrochemical activation of non-noble metal catalyst films.


Mayo, 2015 | DOI: 10.1039/c4cy01524j

STEM-in-SEM high resolution imaging of gold nanoparticles and bivalve tissues in bioaccumulation experiments


C.A. García-Negrete; M.C. Jiménez de Haro; J. Blasco; M. Soto; A. Fernández
Analyst, 140 (2015) 3082-3089

ABSTRACT

The methodology termed scanning transmission electron microscopy in scanning electron microscopy (STEM-in-SEM) has been used in this work to study the uptake of citrate stabilized gold nanoparticles (AuNPs) (average particle sizes of 23.5 ± 4.0 nm) into tissue samples uponin vitro exposure of the dissected gills of the Ruditapes philippinarum marine bivalve to the nanoparticle suspensions. The STEM-in-SEM methodology has been optimized for achieving optimum resolution under SEM low voltage operating conditions (20–30 kV). Based on scanning microscope assessments and resolution testing (SMART), resolutions well below 10 nm were appropriately achieved by working at magnifications over 100k×, with experimental sample thickness between 300 and 200 nm. These relatively thick slices appear to be stable under the beam and help avoid NP displacement during cutting. We herein show that both localizing of the internalized nanoparticles and imaging of ultrastructural disturbances in gill tissues are strongly accessible due to the improved resolution, even at sample thicknesses higher than those normally employed in standard TEM techniques at higher voltages. Ultrastructural imaging of bio-nano features in bioaccumulation experiments have been demonstrated in this study.


Mayo, 2015 | DOI: 10.1039/C4AN01643B

Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors


Roales, Javier; Pedrosa, Jose M.; Guillen, Maria G.; Lopes-Costa, Tania; Castillero, Pedro; Barranco, Angel; Gonzalez-Elipe, Agustin R.
Sensors, 15 (2015) 11118-11132

ABSTRACT

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO2 microstructured columns as a host matrix and its influence on NO2 sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 composite films has revealed that m-TCPP/TiO2 films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO2 through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 films to NO2 has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO2 sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO2 confirm the potential of m-TCPP as a NO2 sensor.


Mayo, 2015 | DOI: 10.3390/s150511118

Self-lubricity of WSex nanocomposite coatings


S. Dominguez-Meister; M. Conte; A. Igartua; T.C. Rojas; J.C. Sánchez-López
ACS Applied Materials & Interfaces, 7 (2015) 7979-7986

ABSTRACT

Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSex coating with low friction (0.07) and low wear rates (3 × 10–7 mm3 Nm–1) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10–8 mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe2 lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe2 phase from oxidation. The increase of the WSe2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.


Abril, 2015 | DOI: 10.1021/am508939s

Hydrogen production through sodium borohydride ethanolysis


Arzac, GM; Fernandez, A
International Journal of Hydrogen Energy, 40 (2015) 5326-5332

ABSTRACT

In this work, sodium borohydride (SB) ethanolysis was explored for the first time as a method to generate hydrogen for Polymer Exchange Membrane Fuel Cells. Ethanolysis by-product was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Nuclear Magnetic Resonance. Metal and acid catalysts were tested. RuCl3 center dot 3H(2)O was the best metal catalyst. Acetic acid was selected for the study because of its effectiveness, low cost and relative greenness. The maximum gravimetric hydrogen density obtained was 2.1% wt. The addition of water produces an increase in hydrogen generation rate and a decrease in conversion. The use of ethanol-methanol mixtures produces an increase in reaction rates in absence of catalyst. As a proof of concept the reaction was performed in a small reactor which operates by the addition of ethanolic acetic acid solutions to solid SB (in the form of granules). The reactor produces stable and constant hydrogen generation in the range of 20-80 ml min(-1) during 1 h at constant temperature (around 27-35 degrees.


Abril, 2015 | DOI: 10.1016/j.ijhydene.2015.01.115

Nanocolumnar coatings with selective behavior towards osteoblast and Staphylococcus aureus proliferation


Izquierdo-Barba, Isabel; Miguel Garcia-Martin, Jose; Alvarez, Rafael; Palmero, Alberto; Esteban, Jaime; Perez-Jorge, Concepcion; Arcos, Daniel; Vallet-Regi, Maria
Acta Biomaterialia, 15 (2015) 20-28

ABSTRACT

Bacterial colonization and biofilm formation on orthopedic implants is one of the worst scenarios in orthopedic surgery, in terms of both patient prognosis and healthcare costs. Tailoring the surfaces of implants at the nanoscale to actively promote bone bonding while avoiding bacterial colonization represents an interesting challenge to achieving better clinical outcomes. Herein, a Ti6Al4V alloy of medical grade has been coated with Ti nanostructures employing the glancing angle deposition technique by magnetron sputtering. The resulting surfaces have a high density of nanocolumnar structures, which exhibit strongly impaired bacterial adhesion that inhibits biofilm formation, while osteoblasts exhibit good cell response with similar behavior to the initial substrates. These results are discussed on the basis of a "lotus leaf effect" induced by the surface nanostructures and the different sizes and biological characteristics of osteoblasts and Staphylococcus aureus.


Marzo, 2015 | DOI: 10.1016/j.actbio.2014.12.023

High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance


Maddi, C; Donnet, C; Loir, AS; Tite, T; Barnier, V; Rojas, TC; Sanchez-Lopez, JC; Wolski, K; Garrelie, F
Applied Surface Science, 332 (2015) 346-353

ABSTRACT

Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen plasma.


Marzo, 2015 | DOI: 10.1016/j.apsusc.2015.01.123

Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects


Lionel C. Gontard, Rafal E. Dunin-Borkowski
Micron

ABSTRACT

High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.


Marzo, 2015 | DOI: 10.1016/j.micron.2014.12.001

Laser Treatment of Ag@ZnO Nanorods as Long-Life-Span SERS Surfaces


Macias-Montero, M; Pelaez, RJ; Rico, VJ; Saghi, Z; Midgley, P; Afonso, CN; Gonzalez-Elipe, AR; Borras, A
ACS Applied Materials & Interfaces, 7 (2015) 2331-2339

ABSTRACT

UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.


Febrero, 2015 | DOI: 10.1021/am506622x

STEM-EELS analysis reveals stable highdensity He in nanopores of amorphous silicon coatings deposited by magnetron sputtering


Schierholz, Roland; Lacroix, Bertrand; Godinho, Vanda; Caballero-Hernandez, Jaime; Duchamp, Martial; Fernandez, Asuncion
Nanotechnology, 26 (2015) 075703

ABSTRACT

A broad interest has been showed recently on the study of nanostructuring of thin films and surfaces obtained by low-energy He plasma treatments and He incorporation via magnetron sputtering. In this paper spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope is used to locate and characterize the He state in nanoporous amorphous silicon coatings deposited by magnetron sputtering. A dedicated MATLAB program was developed to quantify the helium density inside individual pores based on the energy position shift or peak intensity of the He K-edge. A good agreement was observed between the high density (~35–60 at nm−3) and pressure (0.3–1.0 GPa) values obtained in nanoscale analysis and the values derived from macroscopic measurements (the composition obtained by proton backscattering spectroscopy coupled to the macroscopic porosity estimated from ellipsometry). This work provides new insights into these novel porous coatings, providing evidence of high-density He located inside the pores and validating the methodology applied here to characterize the formation of pores filled with the helium process gas during deposition. A similar stabilization of condensed He bubbles has been previously demonstrated by high-energy He ion implantation in metals and is newly demonstrated here using a widely employed methodology, magnetron sputtering, for achieving coatings with a high density of homogeneously distributed pores and He storage capacities as high as 21 at%.


Febrero, 2015 | DOI: 10.1088/0957-4484/26/7/075703

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance


Longtin, R; Sanchez-Valencia, JR; Shorubalko, I; Furrer, R; Hack, E; Elsener, H; Groning, O; Greenwood, P; Rupesinghe, N; Teo, K; Leinenbach, C; Groning, P
Science and Technology of Advanced Materials, 16 (2015) 015005 (11 pp)

ABSTRACT

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 degrees C with a Ag-Cu-Ti alloy and at 880 degrees C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Omega. The improved interfacial transport properties in the brazed films lead to superior electron fieldemission properties when compared to the as-grown films. An emission current of 150 mu A was drawn from the brazed nanotubes at an applied electric field of 0.6 V mu m(-1). The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.


Febrero, 2015 | DOI: 10.1088/1468-6996/16/1/015005

Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions


Gracia-Escosa, E; Garcia, I; Sanchez-Lopez, JC; Abad, MD; Mariscal, A; Arenas, MA; de Damborenea, J; Conde, A
Surface & Coatings Technology, 263 (2015) 78-85

ABSTRACT

Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 026 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia I vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (similar to 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.


Febrero, 2015 | DOI: 10.1016/j.surfcoat.2014.12.047

Sonogashira Cross-Coupling and Homocoupling on a Silver Surface: Chlorobenzene and Phenylacetylene on Ag(100)


Sanchez-Sanchez, C; Orozco, N; Holgado, JP; Beaumont, SK; Kyriakou, G; Watson, DJ; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM
Journal of the American Chemical Society, 137 (2015) 940-947

ABSTRACT

Scanning tunneling microscopy, temperature-programmed reaction, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations were used to study the adsorption and reactions of phenylacetylene and chlorobenzene on Ag(100). In the absence of solvent molecules and additives, these molecules underwent homocoupling and Sonogashira cross-coupling in an unambiguously heterogeneous mode. Of particular interest is the use of silver, previously unexplored, and chlorobenzene—normally regarded as relatively inert in such reactions. Both molecules adopt an essentially flat-lying conformation for which the observed and calculated adsorption energies are in reasonable agreement. Their magnitudes indicate that in both cases adsorption is predominantly due to dispersion forces for which interaction nevertheless leads to chemical activation and reaction. Both adsorbates exhibited pronounced island formation, thought to limit chemical activity under the conditions used and posited to occur at island boundaries, as was indeed observed in the case of phenylacetylene. The implications of these findings for the development of practical catalytic systems are considered.


Enero, 2015 | DOI: 10.1021/ja5115584

"In Operando" X-ray Absorption Spectroscopy Analysis of Structural Changes During Electrochemical Cycling of WO3 and WxSiyOz Amorphous Electrochromic Thin Film Cathodes


Garcia-Garcia, FJ; Gil-Rostra, J; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Chaboy, J
Journal of Physical Chemistry C, 119 (2015) 644-652

ABSTRACT

This work reports a X-ray absorption spectroscopy (XAS) study under in operando conditions of the structural and chemical changes undergone by WO3 and WxSiyOz thin films used as electrochromic cathodes. The electrochromic films were prepared by magnetron sputtering deposition at oblique angles and then characterized by a large variety of techniques. The voltammograms and chronoamperometric diagrams in both aqueous and organic electrolyte media revealed a total reversibility of the electrochromic behavior, a low response time, and a high coloration efficiency for the two types of thin films. The in operando X-ray absorption study of the films working in aqueous solutions revealed that when they were electrochemically cycled the average WO distances reversibly varied by a Delta d of 0.06 and 0.08 angstrom for, respectively, WO3 and WxSiyOz. These changes are discussed by assuming the reduction of W6+ cations and the transformation of W-O double bonds into single WO bond structures during the electrochemical cycling of the films.


Enero, 2015 | DOI: 10.1021/jp508377v

Biotribological behavior of Ag–ZrCxN1−x coatings against UHMWPE for joint prostheses devices


Calderon, SV; Sanchez-Lopez, JC; Cavaleiro, A; Carvalho, S
Journal of the Mechanical Behavior of Biomedical Materials, 41 (2015) 83-91

ABSTRACT

This study aims to evaluate the structural, mechanical and tribological properties of zirconium carbonitrides (ZrCxN1−x) coatings with embedded silver nanoparticles, produced with the intention of achieving a material with enhanced multi-functional properties, including mechanical strength, corrosion resistance, tribological performance and antibacterial behavior suitable for their use in joint prostheses. The coatings were deposited by direct current (DC) reactive magnetron sputtering onto 316 L stainless steel, changing the silver content from 0 to 20 at% by modifying the current density applied to the targets. Different nitrogen and acetylene gas fluxes were used as reactive gases. The coatings revealed different mixtures of crystalline ZrCxN1−x, silver nanoparticles and amorphous carbon phases. The hardness of the films was found to be mainly controlled by the ratio between the hard (ZrCxN1−x) and soft (Ag and amorphous carbon) phases in the films, fluctuating between 7.4 and 20.4 GPa. The coefficient of friction, measured against ultra-high molecular weight polyethylene (UHMWPE) in Hank’s balanced salt solution with 10 g L−1albumin, is governed by the surface roughness and hardness. The UHMWPE wear rates were in the same order of magnitude (between 1.4 and 2.0×10−6 mm3 N−1 m−1), justified by the effect of the protective layer of albumin formed during the tests. The small differences were due to the hydrophobic/hydrophilic character of the surface, as well as to the silver content.


Enero, 2015 | DOI: 10.1016/j.jmbbm.2014.09.028

Uniform, luminescent Eu: LuF3 nanoparticles


Becerro, AI; Gonzalez-Mancebo, D; Ocana, M
Journal of Nanoparticle Research, 17 (2015) 58

ABSTRACT

A simple procedure for the synthesis of orthorhombic, uniform, LuF3 particles with two different morphologies (rhombus- and cocoon-like) and nanometer and sub-micrometer size, respectively, is reported. The method consists in the aging, at 120 °C for 2 h, a solution containing [BMIM]BF4 ionic liquid (0.5 mL) and lutetium acetate (in the case of the rhombi) or lutetium nitrate (in the case of the cocoons) (0.02 M) in ethylene glycol (total volume 10 mL). This synthesis method was also adequate for the synthesis of Eu3+-doped LuF3 particles of both morphologies, whose luminescence properties were investigated in detail. The experimental observations reported herein suggest that these materials are suitable phosphors for optoelectronic as well as in vitro biotechnological applications.


Enero, 2015 | DOI: 10.1007/s11051-015-2874-z

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid


Garcia-Garcia, FJ, Chiu, TY, Skeldon, P, Thompson, GE
Surface and Interface Analysis, 47 (2015) 30-36

ABSTRACT

Cathodic polarization of aluminium and Al-0.18wt.%Mg and Al-0.08wt.% Ti alloys in 0.24moldm(-3) nitric acid solution at 38 degrees C has been employed to assist understanding of the roles of alloying elements in electrograining. The findings indicate that additions of magnesium and titanium to aluminium accelerate the corrosion of the substrate under the alkalization caused by the cathodic reactions. The accelerated dissolution and the consequent formation of hydrated alumina result in a decreased net cathodic current density in potentiostatic and potentiodynamic polarization conditions relative to the behaviour of aluminium. 


Enero, 2015 | DOI: 10.1002/sia.5640



2014


Quinone-Rich Poly(dopamine) Magnetic Nanoparticles for Biosensor Applications


Martin, M; Orive, AG; Lorenzo-Luis, P; Creus, AH; Gonzalez-Mora, JL; Salazar, P
ChemPhysChem, 15 (2014) 3742-3752

ABSTRACT

Novel core-shell quinone-rich poly(dopamine)–magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier-transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer-film thickness of 2 nm. The core-shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA m−1 cm−2, a low limit of detection (0.02 mm), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer.


Diciembre, 2014 | DOI: 10.1002/cphc.201402417

LMM Auger primary excitation spectra of copper


Pauly, N; Tougaard, S; Yubero, F
Surface Science, 630 (2014) 294-299

ABSTRACT

The shape and intensity of measured Auger peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and to intrinsic excitations induced by the sudden creation of the two static core holes. Following a method developed for XPS in a previous work [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17], we have calculated the effective energy-differential inelastic electron scattering cross-sections, including the effects of the surface and of the two core holes, within the dielectric response theory by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS). The Auger spectra are then modeled by convoluting this energy loss cross section with the primary excitation spectrum that accounts for all effects which are part of the initial Auger process, i.e. L–S coupling and vacancy satellite effects. The shape of this primary excitation spectrum is fitted to get close agreement between the theoretical and the experimental spectra obtained from X-ray excited Auger electron spectroscopy (XAES). We have performed these calculations of XAES spectra for various LMM Auger transitions of pure Cu (L3M45M45, L3M23M45, L3M23M23 and L2M45M45 transitions). We compare the resulting primary excitation spectra with theoretical results published in the literature and obtain reasonable quantitative agreement. In particular, we extract from experimental spectra quantitative intensities due to Coster–Kronig, shake-off and shake-up processes relative to the intensity from the “normal” Auger process.


Diciembre, 2014 | DOI: 10.1016/j.susc.2014.08.029

Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): Structure and electron irradiation effects


Gontard, LC; Fernandez, A; Dunin-Borkowski, RE; Kasama, T; Lozano-Perez, S; Lucas, S
Micron, 67 (2014) 1-9

ABSTRACT

Hybrid (organic shell–inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed.


Diciembre, 2014 | DOI: 10.1016/j.micron.2014.06.004

Chemistry, nanostructure and magnetic properties of Co-Ru-B-O nanoalloys


Arzac, GM; Rojas, TC; Gontard, LC; Chinchilla, LE; Otal, E; Crespo, P; Fernandez, A
RSC Advances, 4 (2014) 46576-46586

ABSTRACT

In our previous works, Co–B–O and Co–Ru–B–O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co–Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co–Ru–B–O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1−x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure–performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru–B–O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co–B–O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1−x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series.


Noviembre, 2014 | DOI:

Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis


Paladini, M; Arzac, GM; Godinho, V; De Haro, MCJ; Fernandez, A
Applied Catalysis B: Environmental, 158-159 (2014) 400-409

ABSTRACT

Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50 W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5 × 10−2 to 4.5 × 10−2 mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650 ml min−1 gcat−1 for the 50 W Co 4.5 (4 h) sample (Ea = 60 ± 2 kJ mol−1). For AB hydrolysis activity for the 50 W Co 3.2 (4 h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong Co–NH3 interactions explain the non-efficiency of the acid washing.


Octubre, 2014 | DOI: 10.1016/j.apcatb.2014.04.047

Shape-defined nanodimers by tailored heterometallic epitaxy


Garcia-Negrete, Carlos A; Rojas, Teresa C; Knappett, Benjamin R; Jefferson, David A; Wheatley, Andrew E H; Fernandez, Asuncion
Nanoscale, 6 (2014) 11090-11097

ABSTRACT

The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.


Octubre, 2014 | DOI: 10.1039/C4NR01815J

The Use of Fluorocarbons to Mitigate the Oxygen Dependence of Glucose Microbiosensors for Neuroscience Applications


Martin, M; O'Neill, RD; Gonzalez-Mora, JL; Salazar, P
Journal of The Electrochemical Society, 161 (2014) H689-H695

ABSTRACT

First-generation amperometric glucose biosensors are the most commonly used method for glucose monitoring in neuroscience. Nevertheless, biosensors of this genre suffer from the so-called "oxygen deficit". This problem is particularly acute when the oxygen concentration is low, as is the case in brain extracellular fluid. In the present work we use different fluorocarbons, such as Nafion and H700, to mitigate the oxygen deficit. These fluorocarbon-derived materials display a remarkable solubility for oxygen, and are able to act as oxygen reservoirs supporting the enzymatic reaction. Different biosensor configurations are presented, evaluating their sensitivity, linear range and oxygen dependence. Optimized Nafion- and H700-modified biosensors displayed a remarkable oxygen tolerance, with K-M(O-2) values as low as 11 and 4 mu mol L-1, respectively, and an appropriate sensitivity for in-vivo applications. Finally, in-vivo data are reported in order to illustrate the application of such devices in neuroscience applications.


Octubre, 2014 | DOI: 10.1149/2.1071410jes

Tribological comparison of different C-based coatings in lubricated and unlubricated conditions


Ciarsolo, I; Fernandez, X; de Gopegui, UR; Zubizarreta, C; Abad, MD; Mariscal, A; Caretti, I; Jimenez, I; Sanchez-Lopez, JC
Surface and Coatings Technology, 257 (2014) 278-285

ABSTRACT

The use of carbon-based coatings (hydrogenated and non-hydrogenated DLC, doped and alloyed-DLC) is of wide interest due to its applications in mechanical components submitted to friction and wear including sliding parts in automotive engines. A tribological comparative analysis using a reciprocating (SRV) tester in lubricated and unlubricated conditions with a 4-stroke motor oil has been carried out on six currently relevant state-of-the-art coatings (namely WC/a-C, TiBC/a-C and TiC/a-C:H nanocomposites, Ti-doped DLC, BCN film and a crystalline monolithic TiC film as reference). The quantification of the fraction of the sp(2)-bonded matrix has been done by fitting of C 1s XPS peak and the mechanical properties evaluated by nanoindentation. The comparative analysis has allowed us to identify the capabilities of each system depending on the testing conditions and the possible synergies as a function of the chemical composition and film nature. Under lubricated harsh conditions (max. contact pressure 1.7 GPa) only coatings displaying hardness superior to 20 GPa could stand the sliding motion without failure. At lower contact pressures, a significant fraction of sp(2) carbon (>= 75%) is advantageous for reducing wear in boundary lubrication. WC/a-C, BCN and Ti-DLC films showed the best tribological response in dry sliding conditions. This fundamental information would be of relevance for assisting engineers in selecting best partnership for lubrication systems. 


Octubre, 2014 | DOI: 10.1016/j.surfcoat.2014.07.068

Study of the early stages of growth of Co oxides on oxide substrates


Diaz-Fernandez, D; Mendez, J; Yubero, F; Dominguez-Canizares, G; Gutierrez, A; Soriano, L
Surface and Interface Analysis, 46 (2014) 975-979

ABSTRACT

The growth of Cobalt oxides by reactive thermal evaporation of metallic Cobalt in an oxygen atmosphere on a series of oxide substrates, namely SiO2, Al2O3 and MgO, has been chemically and morphologically studied by means of XPS and atomic force microscopy (AFM). The XPS results reveal that cobalt oxide grows as CoO (Co2+) for coverages up to some tens of equivalent monolayers on all substrates. For larger coverages, the formation of the spinel oxide Co3O4 has been observed. AFM and XPS quantification allowed us to determine the way of growth of CoO on all substrates, being of Volmer-Weber (i.e. islands) mode for SiO2, whereas for Al2O3 and MgO, the growth follows the Frank-van der Merwe (i.e. layer-by-layer) mode. The results are discussed in terms of the mismatch of the lattice parameters of the CoO adsorbates with the substrates


Octubre, 2014 | DOI: 10.1002/sia.5366

Interpretation of electron Rutherford backscattering spectrometry for hydrogen quantification


Alvarez, R; Yubero, F
Surface and Interface Analysis, 46 (2014) 812-816

ABSTRACT

In the last few years, several papers have appeared showing the capabilities of electron Rutherford backscattering spectrometry (eRBS) to quantify the H content at surfaces. The basis of the H detection in this technique relies on the difference in recoil energy of the incident electrons depending on the mass of the atoms located at the surface that act as scatter centers. In this paper, we address the interpretation of eRBS spectra of hydrogen containing surfaces. The aim is to compare the naive single elastic scattering approximation with a more realistic description of eRBS spectra including multiple elastic scattering using the HQ-eRBS (hydrogen quantification eRBS) software based on a Monte Carlo algorithm. It is concluded that multiple elastic scattering is a significant contribution to experimentally measured eRBS spectra of a polyethylene surface. It induces significant broadening of the distribution of the maximum elastic scattering angle along the electron trajectories contributing to the measured spectra. However, it has weak effect in the energy distribution of the collected electrons (about 10% overestimation of the H content in the particular case of a polyethylene surface with respect to the corresponding ratio of elastic scattering cross sections).


Octubre, 2014 | DOI: 10.1002/sia.5486

Modeling of X-ray photoelectron spectra: surface and core hole effects


Pauly, N; Tougaard, S; Yubero, F
Surface and Interface Analysis, 46 (2014) 920-923

ABSTRACT

The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and by intrinsic excitations induced by the sudden creation of the static core hole. Besides, elastic electron scattering may also be important. These effects should be included in the theoretical description of the emitted photoelectron peaks. To investigate the importance of surface and core hole effects relative to elastic scattering effect, we have calculated full XPS spectra for the Cu 2p emissions of Cu and CuO with the simulation of electron spectra for surface analysis (SESSA) software and with a convolution procedure using the differential inelastic electron scattering cross-section obtained with the quantitative analysis of electron energy loss in XPS (QUEELS-XPS) software. Surface and core hole effects are included in QUEELS-XPS but absent in SESSA while elastic electron scattering effects are included in SESSA but absent in QUEELS-XPS. Our results show that the shape of the XPS spectra are strongly modified because of surface and core hole effects, especially for energy losses smaller than about 20eV.


Octubre, 2014 | DOI: 10.1002/sia.5372

Impregnation of carbon black for the examination of colloids using TEM


Gontard, LC; Knappett, BR; Wheatley, AEH; Chang, SLY; Fernandez, A
Carbon, 76 (2014) 464-468

ABSTRACT

Nanoparticles are frequently synthesised as colloids, dispersed in solvents such as water, hexane or ethanol. For their characterisation by transmission electron microscopy (TEM), a drop of colloid is typically deposited on a carbon support and the solvent allowed to evaporate. However, this method of supporting the nanoparticles reduces the visibility of fine atomic details, particularly for carbonaceous species, due to interference from the 2-dimensional carbon support at most viewing angles. We propose here the impregnation of a 3 dimensional carbon black matrix that has been previously deposited on a carbon film as an alternative means of supporting colloidal nanoparticles, and show examples of the application of this method to advanced TEM techniques in the analysis of monometallic, core@shell and hybrid nanoparticles with carbon-based shells.

Nanoparticles represent one of the most studied structures in nanotechnology and nanoscience because of the wide range of applications arising from their unique optical, physical and chemical properties [1]. Often they have core@shell structures, or are coated with organic molecules. Nanoparticle functionality is largely affected by the specific configuration of the outer surface atoms. For example, in heterogeneous catalysis activity and selectivity are mostly determined by the type of atomic defects present at the surface of metallic nanoparticles, and in the field of biomedicine the surface coating of hybrid (inorganic core@organic shell) nanoparticles regulates their stability, solubility and targeting.

Nanoparticles are frequently synthesised using solution techniques that yield colloids, i.e., a solid–liquid mixture containing solid particles that are dispersed to various degrees in a liquid medium; most frequently water, ethanol or hexane. Colloid characterisation generally employs a variety of techniques to establish understanding and control over nanoparticle synthesis and properties. Electron microscopy in transmission mode (TEM) and in scanning transmission mode (STEM) are widely used for particle characterisation, and advances in these techniques mean that it is now routinely possible to resolve single atoms at the surfaces of nanoparticles using aberration-corrected microscopes, to elucidate the three-dimensional shapes of nanoparticles using electron tomography, and to enhance the contrast in very low density materials (e.g., carbonaceous materials) using electron holography [2] and [3]. However, the significant potential of these (S)TEM techniques is ultimately limited by the sample and the techniques available for sample preparation.

Typically, examination by (S)TEM requires that a nanoparticulate sample be prepared by depositing a drop of colloid on a thin, electron-transparent support. It is usual that an amorphous carbon film, silicon nitride film or graphene layers deposited on a copper grid constitute the support [4]. Crucially, these sample preparation techniques suffer from the major limitation that the contrast from the support often shadows atomic details at the particle surface. Moreover, it has been established that the thinnest supports can degrade under electron-beam irradiation, affecting particle stability [5], and also that hydrocarbon contamination can be an issue [6]. The most widely used commercially available TEM support is holey carbon, which comprises of a perforated carbon thin film. In this case, sample preparation aims to locate at least some of the nanoparticles of interest at the edges of the perforations. However, the concave nature of the holes means that solvent contaminants tend to accumulate preferentially at these sites. Moreover, if the TEM sample holder is tilted a particle attached to the edge of a hole is very likely to be shadowed by the carbon film. Taken together, these drawbacks significantly limit the application of techniques such as electron tomography [6].

We propose here a method of circumventing some of these fundamental problems by developing a technique for mounting nanoparticulate samples using a carbon matrix that is inspired by the way samples used in electrocatalysis are prepared [7]. Fig. 1 shows an image of a typical Pt-based electrocatalyst supported on carbon black as used in proton-electron membrane fuels cells, and which consists of Pt nanoparticles formed by calcination of a carbon black impregnated with a solution of salt precursor. Carbon black is a low-grade form of graphite, which is composed of nanocrystallites and no long-range order [8]. In Fig. 1 the carbon black is Vulcan XC-72R, which is widely used as a catalyst support in fuel cells because it provides high electrical conductivity, good reactant gas access, adequate water handling and good corrosion resistance, whilst allowing high dispersion of the particles. In electrocatalyst samples it is common to find particles, like the 5 nm Pt particle shown in Fig. 1, attached strongly to the surface of the support and viewed edge-on against a vacuum so as to provide optimal conditions for high-resolution TEM (HRTEM). Fig. 1B is a quantitative phase image of a Pt particle obtained from a defocus series of 20 images at intervals of 5 nm acquired in a FEGTEM JEOL 2020 at 200 kV with spherical aberration of −30 μm and applying the exit-wave restoration technique [2]. The contrast between details of the particle finestructure is very high compared to conventional HRTEM images, and details such as the presence of monoatomic carbon ribbons surrounding the particle can be seen.


Septiembre, 2014 | DOI: 10.1016/j.carbon.2014.05.006

On the formation of the porous structure in nanostructured a-Si coatings deposited by dc magnetron sputtering at oblique angles


Godinho, V; Moskovkin, P; Alvarez, R; Caballero-Hernandez, J; Schierholz, R; Bera, B; Demarche, J; Palmero, A; Fernandez, A; Lucas, S
Nanotechnology, 25 (2014) 355705

ABSTRACT

The formation of the porous structure in dc magnetron sputtered amorphous silicon thin films at low temperatures is studied when using helium and/or argon as the processing gas. In each case, a-Si thin films were simultaneously grown at two different locations in the reactor which led to the assembly of different porous structures. The set of four fabricated samples has been analyzed at the microstructural level to elucidate the characteristics of the porous structure under the different deposition conditions. With the help of a growth model, we conclude that the chemical nature of the sputter gas not only affects the sputtering mechanism of Si atoms from the target and their subsequent transport in the gaseous/plasma phase towards the film, but also the pore formation mechanism and dynamics. When Ar is used, pores emerge as a direct result of the shadowing processes of Si atoms, in agreement with Thornton's structure zone model. The introduction of He produces, in addition to the shadowing effects, a new process where a degree of mobility results in the coarsening of small pores. Our results also highlight the influence of the composition of sputtering gas and tilt angles (for oblique angle deposition) on the formation of open and/or occluded porosity.


Septiembre, 2014 | DOI: 10.1088/0957-4484/25/35/355705

Reticulated bioactive scaffolds with improved textural properties for bone tissue engineering: Nanostructured surfaces and porosity


Ramiro-Gutierrez, ML; Will, J; Boccaccini, AR; Diaz-Cuenca, A
Journal of Biomedical Materials Research Part A, 102 (2014) 2982-2992

ABSTRACT

Organised nanoporous SBA-15 type silica precursor (SP) particulate material has been processed into three-dimensional macroporous, reticulated structures using a novel strategy consisting of blending increasing percentages of SP with a SiO2-CaO-P2O5 (80Si15Ca5P) mesoporous bioactive glass (MBG) sol. The procedure successfully produced consolidated and functionally competent open-cell scaffolds while preserving the nanoporous order of the SP. Scaffolds were prepared using four different (MBG)/(SP) ratios. These structures were then characterized using field emission gun scanning electron microscopy, X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and compressive strength testing. Open-cell interconnected structures with dual macro (150-500 mu m) and nano (4-6 nm)-organised porosity were produced. Both the textural and mechanical properties were found to improve with increasing SBA-15 content. The in vitro bioactive response using simulated body fluid confirmed high reactivity for all prepared scaffolds. In addition, the SBA-15 containing scaffolds exhibited a superior ability to delay the pH-triggered lysozyme release with antibiotic activity. (C) 2013 Wiley Periodicals, Inc.


Septiembre, 2014 | DOI: 10.1002/jbm.a.34968

Bending Induced Self-Organized Switchable Gratings on Polymeric Substrates


Parra-Barranco, J; Oliva-Ramirez, M; Gonzalez-Garcia, L; Alcaire, M; Macias-Montero, M; Borras, A; Frutos, F; Gonzalez-Elipe, AR; Barranco, A
ACS Applied Materials & Interfaces, 6 (2014) 11924-11931

ABSTRACT

We present a straightforward procedure of self-surface patterning with potential applications as large area gratings, invisible labeling, optomechanical transducers, or smart windows. The methodology is based in the formation of parallel micrometric crack patterns when polydimethylsiloxane foils coated with tilted nanocolumnar SiO2 thin films are manually bent. The SiO2 thin films are grown by glancing angle deposition at room temperature. The results indicate that crack spacing is controlled by the film nanostructure independently of the film thickness and bending curvature. They also show that the in-plane microstructural anisotropy of the SiO2 films due to column association perpendicular to the growth direction determines the anisotropic formation of parallel cracks along two main axes. These self-organized patterned foils are completely transparent and work as customized reversible diffraction gratings under mechanical activation.


Agosto, 2014 | DOI: 10.1021/am5037687

Luminescent 3-hydroxyflavone nanocomposites with a tuneable refractive index for photonics and UV detection by plasma assisted vacuum deposition


Aparicio, FJ; Alcaire, M; Borras, A; Gonzalez, JC; Lopez-Arbeloa, F; Blaszczyk-Lezak, I; Gonzalez-Elipe, AR; Barranco, A
Journal of Materials Chemistry C, 2 (2014) 6561-6573

ABSTRACT

Luminescent organic-thin-films transparent in the visible region have been synthesized by a plasma assisted vacuum deposition method. The films have been developed for their implementation in photonic devices and for UV detection. They consist of a plasma polymeric matrix that incorporates 3-hydroxyflavone molecules characterized by absorption of UV radiation and emission of green light. The present work studies in detail the properties and synthesis of this kind of transparent and luminescent material. The samples were characterized by X-ray photoemission (XPS), infrared (FT-IR) and secondary ion mass (ToF-SIMS) spectroscopies; and their optical properties were analysed by UV-Vis absorption, fluorescence and ellipsometry (VASE) spectroscopies. The key factors controlling the optical and luminescent properties of the films are also discussed. Indeed, our experimental results show how the optical properties of the films can be adjusted for their integration in photonic devices. Moreover, time resolved and steady state fluorescence analyses, including quantum yield determination, indicate that the fluorescence efficiency is a function of the deposition parameters. An outstanding property of these materials is that, even for high UV absorption values (i.e. large layer thickness and/or dye concentration), the emitted light is not reabsorbed by the film. Such highly UV absorbent and green emitting films can be used as UV photodetectors with a detection threshold smaller than 10 mu W cm(-2), a value similar to the limit of some commercial UV photodetectors. Based on these properties, the use of the films as visual tags for the detection of solar UV irradiation is proposed.


Agosto, 2014 | DOI: 10.1039/c4tc00294f

Chromium removal on chitosan-based sorbents - An EXAFS/XANES investigation of mechanism


Vieira, RS; Meneghetti, E; Baroni, P; Guibal, E; de la Cruz, VMG; Caballero, A; Rodriguez-Castellon, E; Beppu, MM
Materials Chemistry and Physics, 146 (2014) 412-417

ABSTRACT

Chitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds – resulting from the reaction of the crosslinking agent and amino groups – may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction.


Agosto, 2014 | DOI: 10.1016/j.matchemphys.2014.03.046

Simultaneous quantification of light elements in thin films deposited on Si substrates using proton EBS (Elastic Backscattering Spectroscopy)


Ferrer, FJ; Alcaire, M; Caballero-Hernandez, J; Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Godinho, V; Garcia-Lopez, J; Barranco, A; Fernandez-Camacho, A
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 332 (2014) 449-453

ABSTRACT

Quantification of light elements content in thin films is an important and difficult issue in many technological fields such as polymeric functional thin films, organic thin film devices, biomaterials, and doped semiconducting structures.
Light elements are difficult to detect with techniques based on X-ray emission, such as energy dispersive analysis of X-rays (EDAX). Other techniques, like X-ray photoelectron spectroscopy (XPS), can easily quantify the content of light elements within a surface but often these surface measurements are not representative of the lights elements global composition of the thin film. Standard Rutherford backscattering spectroscopy (RBS), using alpha particles as probe projectiles, is not a good option to measure light elements deposited on heavier substrates composed of heavier elements like Si or glass. Nuclear Reaction Analysis (NRA) offers a good quantification method, but most of the nuclear reactions used are selective for the quantification of only one element, so several reactions and analysis are necessary to measure different elements.
In this study, Elastic Backscattering Spectroscopy (EBS) using proton beams of 2.0 MeV simultaneously quantified different light elements (helium, carbon, nitrogen, oxygen, and fluorine) contained in thin films supported on silicon substrates. The capabilities of the proposed quantification method are illustrated with examples of the analysis for a series of thin film samples: amorphous silicon with helium bubbles, fluorinated silica, fluorinated diamond-like carbon and organic thin films. It is shown that this simple and versatile procedure allows the simultaneous quantification of light elements in thin films with thicknesses in the 200–500 nm range and contents lower than 10 at.%.


Agosto, 2014 | DOI: 10.1016/j.nimb.2014.02.124

Bifunctional, Monodisperse BiPO4-Based Nanostars: Photocatalytic Activity and Luminescent Applications


Becerro, AI; Criado, J; Gontard, LC; Obregon, S; Fernandez, A; Colon, G; Ocana, M
Crystal Growth & Design, 14 (2014) 3319-3326

ABSTRACT

Monodisperse, monoclinic BiPO4 nanostars have been synthesized by a homogeneous precipitation reaction at 120 °C through controlled release of Bi3+ cations from a Bi–citrate chelate, in a mixture of glycerol and ethylene glycol, using H3PO4 as the phosphate source. The set of experimental conditions necessary to obtain uniform nanoparticles is very restrictive, as the change in either the polyol ratio or the reactant concentrations led to ill-defined and/or aggregated particles. The morphology of the particles consists of a starlike, hierarchical structure formed by the ordered arrangement of nanorod bundles. Transmission electron tomography has revealed that the nanostars are not spherical but flattened particles. Likewise, Fourier transform infrared spectroscopy and thermogravimetry have shown that the synthesized nanostars are functionalized with citrate groups. The mechanism of formation of the nanostars has been analyzed to explain their morphological features. The as-synthesized BiPO4 nanostars exhibit an efficient photocatalytic performance for the degradation of Rhodamine B. Finally, it has been demonstrated that the stars can be Eu3+-doped up to 2 mol % without any change in the particle morphology or symmetry, and the doped samples show emission in the orange-red region of the visible spectrum after ultraviolet excitation. These experimental observations make this material a suitable phosphor for biotechnological applications.


Julio, 2014 | DOI: 10.1021/cg500208h

Influence of thickness and coatings morphology in the antimicrobial performance of zinc oxide coatings


Carvalho, P; Sampaio, P; Azevedo, S; Vaz, C; Espinos, JP; Teixeira, V; Carneiro, JO
Applied Surface Science, 307 (2014) 548-557

ABSTRACT

In this research work, the production of undoped and silver (Ag) doped zinc oxide (ZnO) thin films for food-packaging applications were developed. The main goal was to determine the influence of coatings morphology and thickness on the antimicrobial performance of the produced samples. The ZnO based thin films were deposited on PET (Polyethylene terephthalate) substrates by means of DC reactive magnetron sputtering. The thin films were characterized by optical spectroscopy, X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The antimicrobial performance of the undoped and Ag-doped ZnO thin films was also evaluated. The results attained have shown that all the deposited zinc oxide and Ag-doped ZnO coatings present columnar morphology with V-shaped columns. The increase of ZnO coatings thickness until 200 nm increases the active surface area of the columns. The thinner samples (50 and 100 nm) present a less pronounced antibacterial activity than the thickest ones (200–600 nm). Regarding Ag-doped ZnO thin films, it was verified that increasing the silver content decreases the growth rate of Escherichia coli and decreases the amount of bacteria cells present at the end of the experiment


Julio, 2014 | DOI: 10.1016/j.apsusc.2014.04.072

Nanocolumnar growth of thin films deposited at oblique angles: Beyond the tangent rule


Alvarez, R; Lopez-Santos, C; Parra-Barranco, J; Rico, V; Barranco, A; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Vacuum Science & Technology B, 32 (2014) 041802

ABSTRACT

The growth of nanostructured physical vapor deposited thin films at oblique angles is becoming a hot topic for the development of a large variety of applications. Up to now, empirical relations, such as the so-called tangent rule, have been uncritically applied to account for the development of the nanostructure of these thin films even when they do not accurately reproduce most experimental results. In the present paper, the growth of thin films at oblique angles is analyzed under the premises of a recently proposed surface trapping mechanism. The authors demonstrate that this process mediates the effective shadowing area and determines the relation between the incident angle of the deposition flux and the tilt angle of the columnar thin film nanostructures. The analysis of experimental data for a large variety of materials obtained in our laboratory and taken from the literature supports the existence of a connection between the surface trapping efficiency and the metallic character of the deposited materials. The implications of these predictive conclusions for the development of new applications based on oblique angle deposited thin films are discussed.


Julio, 2014 | DOI: 10.1116/1.4882877

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques


Lapresta-Fernandez, A; Salinas-Castillo, A; de la Llana, SA; Costa-Fernandez, JM; Dominguez-Meister, S; Cecchini, R; Capitan-Vallvey, LF; Moreno-Bondi, MC; Marco, MP; Sanchez-Lopez, JC; Anderson, IS
Critical Reviews in Solid State and Materials Sciences, 39 (2014) 423-458

ABSTRACT

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.


Junio, 2014 | DOI: 10.1080/10408436.2014.899890

The Flexible Surface Revisited: Adsorbate-Induced Reconstruction, Homocoupling, and Sonogashira Cross-Coupling on the Au(100) Surface


Sanchez-Sanchez, C; Yubero, F; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM
Journal of Physical Chemistry C, 118 (2014) 11677-11684

ABSTRACT

Phenylacetylene (PA) and iodobenzene (IB) are prototypical reactants in Sonogashira cross-coupling. Their adsorption behavior and reactivity on the Au(100) surface were studied by STM, temperature-programmed desorption and reaction, and DFT calculations that included the effect of dispersion forces. The two species exhibited very different behavior. Thus, even at 200 K, PA rearranged Au surface atoms so as to lift the hex reconstruction and adsorb in 4-fold-symmetric islands on the unreconstructed 100 surface. On the other hand, IB adsorbed on the reconstructed hex surface, again as islands, forming three different coexisting close-packed structures. The DFT results are in good accord with these findings, demonstrating the strong preference of PA and IB for the (100) and hex surfaces, respectively. Moreover, the calculated adsorption energies were in satisfactory agreement with values estimated from the desorption data. Adsorbed separately, both PA and IB underwent homocoupling yielding diphenyl diacetylene and biphenyl, respectively; in the former case, reaction appeared to originate at island boundaries. On the well-annealed surface, coadsorbed PA and IB behaved independently, generating only products of homocoupling. However, on the Ar+ roughened surface, Sonogashira cross-coupling also occurred, yielding diphenyl acetylene. These findings are discussed in terms of the island-forming propensity of the reactants, amplified by the labile nature of the Au 100 surface under adsorption and the marked preference of the two reactants for different substrate structures, factors that act to inhibit the formation of a mixed adlayer and suppress reactivity. The implications for the behavior of practical Au nanoparticle catalysts are considered.


Junio, 2014 | DOI: 10.1021/jp501321u

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania


Lv, YK; Cheng, J; Matthews, PD; Holgado, JP; Willkomm, J; Leskes, M; Steiner, A; Fenske, D; King, TC; Wood, PT; Gan, LH; Lambert, RM; Wright, DS
Dalton Transactions, 43 (2014) 8679-8689

ABSTRACT

To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).


Junio, 2014 | DOI: 10.1039/C4DT00555D

On the Deposition Rates of Magnetron Sputtered Thin Films at Oblique Angles


Alvarez, R; Garcia-Martin, JM; Lopez-Santos, MC; Rico, V; Ferrer, FJ; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Plasma Processes and Polymers, 11 (2014) 571-576

ABSTRACT

We describe here the deposition of thin films using magnetron sputtering at oblique angles. General relations between the deposition rates of the films and experimental parameters, such as gas pressure or substrate tilt angles, are deduced and experimentally tested. The model also permits the direct determination of the thermalization mean free path of the sputtered particles in the plasma gas, a key parameter defining the balance between ballistic and diffusive flows in the deposition reactor. The good agreement between experimental and calculated results supports the validity of our description, which becomes a useful tool to explain the main features of the magnetron sputtering deposition of thin films at oblique angles.


Junio, 2014 | DOI: 10.1002/ppap.201300201

The growth of cobalt oxides on HOPG and SiO2 surfaces: A comparative study


Diaz-Fernandez, D; Mendez, J; Bomati-Miguel, O; Yubero, F; Mossanek, RJO; Abbate, M; Dominguez-Canizares, G; Gutierrez, A; Tougaard, S; Soriano, L
Surface Science, 624 (2014) 145-153

ABSTRACT

The growth of cobalt oxides by reactive thermal evaporation of metallic cobalt on highly oriented pyrolytic graphite (HOPG) and SiO2 (X cut quartz surface), in an oxygen atmosphere at room temperature, has been chemically and morphologically studied by means of X-ray photoelectron spectroscopy and atomic force microscopy. The chemical analysis, which also includes cluster calculations, reveals that for the early deposition stages on both substrates, Co2 + species are stabilized at the surface up to a coverage which depends on the substrate. Further coverages lead to the formation of the spinel oxide Co3O4. The results are discussed in terms of the dependence of the surface energy on the size of the CoO deposited moieties. On the other hand, it has been found that the initial way of growth of cobalt oxides on HOPG is of Stranski–Krastanov mode whereas on SiO2 the growth is of Volmer–Weber mode. The differences in the growth morphology have been discussed in terms of the surface diffusivity of the CoO deposits on the substrates.


Junio, 2014 | DOI: 10.1016/j.susc.2014.02.007

Tomographic Heating Holder for In Situ TEM: Study of Pt/C and PtPd/Al2O3 Catalysts as a Function of Temperature


Gontard, LC; Dunin-Borkowski, RE; Fernandez, A; Ozkaya, D; Kasama, T
Microscoy and Microanalysis, 20 (2014) 982-990

ABSTRACT

A tomographic heating holder for transmission electron microscopy that can be used to study supported catalysts at temperatures of up to similar to 1,500 degrees C is described. The specimen is placed in direct thermal contact with a tungsten filament that is oriented perpendicular to the axis of the holder without using a support film, allowing tomographic image acquisition at high specimen tilt angles with minimum optical shadowing. We use the holder to illustrate the evolution of the active phases of Pt nanoparticles on carbon black and PtPd nanoparticles on gamma-alumina with temperature. Particle size distributions and changes in active surface area are quantified from tilt series of images acquired after subjecting the specimens to increasing temperatures. The porosity of the alumina support and the sintering mechanisms of the catalysts are shown to depend on distance from the heating filament.


Junio, 2014 | DOI: 10.1017/S1431927614000373

Oxygen Optical Sensing in Gas and Liquids with Nanostructured ZnO Thin Films Based on Exciton Emission Detection


Sanchez-Valencia, JR; Alcaire, M; Romero-Gomez, P; Macias-Montero, M; Aparicio, FJ; Borras, A; Gonzalez-Elipe, AR; Barranco, A
Journal of Physical Chemistry C, 118 (2014) 9852-9859

ABSTRACT

Transparent nanocolumnar porous ZnO thin films have been prepared by plasma-enhanced chemical vapor deposition. By controlling the H-2/O-2 ratio in the plasma gas, the deposition conditions were optimized to obtain an intense exciton emission at around 381 nm and virtually no luminescence in the visible region associated with electronic states in the gap. The intensity of the exciton band varied significantly and reversibly with the partial pressure of oxygen in the environment. This behavior and its variations with temperature and water vapor sustain the use of these thin films as photonic sensors of oxygen. Further experiments in liquid water show that fluorescence intensity also varies with the amount of dissolved oxygen even for concentrations lower than 0.02 mg/L where commercial oxygen galvanic sensors show limited sensitivity. These results and the use of ZnO as photonic sensor of oxygen are discussed by assuming a classical mechanism involving the photoactivated adsorption of oxygen when this oxide is irradiated with UV light during its fluorescence interrogation.


Mayo, 2014 | DOI: 10.1021/jp5026027

Structure determination and electronic structure of Cu3Au0.5N


Soto, G; Ponce, I; Moreno, MG; Yubero, F; De la Cruz, W
Journal of Alloys and Compounds, 594 (2014) 48-51

ABSTRACT

This study investigated the formation of a Cu3Au-nitride alloy using both experimental and computational methods. The alloy was produced as thin film by sputtering a Cu3Au target in a nitrogen atmosphere. The films were characterized for structure and composition by spectroscopic and diffraction techniques. The structure was established by Rietveld and ab inito methods. The structure is cubic and of the Fm3m space group, with a composition close to Cu6AuN2. Relative to the Cu3N structure, the Cu atoms occupy the faces, Au the half corners, and N the centers. The compound is a narrow-gap semiconductor with a positive hall coefficient that could be used for infrared detection.


Mayo, 2014 | DOI: 10.1016/j.jallcom.2014.01.113

Osteoconductive Potential of Barrier NanoSiO(2) PLGA Membranes Functionalized by Plasma Enhanced Chemical Vapour Deposition


Terriza, A; Vilches-Perez, JI; de la Orden, E; Yubero, F; Gonzalez-Caballero, JL; Gonzalez-Elipe, AR; Vilches, J; Salido, M
BioMed Research International, 2014 (2014) 253590

ABSTRACT

The possibility of tailoring membrane surfaces with osteoconductive potential, in particular in biodegradable devices, to create modified biomaterials that stimulate osteoblast response should make them more suitable for clinical use, hopefully enhancing bone regeneration. Bioactive inorganic materials, such as silica, have been suggested to improve the bioactivity of synthetic biopolymers. An in vitro study on HOB human osteoblasts was performed to assess biocompatibility and bioactivity of SiO2 functionalized poly(lactide-co-glycolide) (PLGA) membranes, prior to clinical use. A 15 nm SiO2 layer was deposited by plasma enhanced chemical vapour deposition (PECVD), onto a resorbable PLGA membrane. Samples were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and infrared spectroscopy (FT-IR). HOB cells were seeded on sterilized test surfaces where cell morphology, spreading, actin cytoskeletal organization, and focal adhesion expression were assessed. As proved by the FT-IR analysis of samples, the deposition by PECVD of the SiO2 onto the PLGA membrane did not alter the composition and other characteristics of the organic membrane. A temporal and spatial reorganization of cytoskeleton and focal adhesions and morphological changes in response to SiO2 nanolayer were identified in our model. The novedous SiO2 deposition method is compatible with the standard sterilization protocols and reveals as a valuable tool to increase bioactivity of resorbable PLGA membranes.


Mayo, 2014 | DOI: 10.1155/2014/253590

Tuning the transmittance and the electrochromic behavior of CoxSiyOz thin films prepared by magnetron sputtering at glancing angle


Gil-Rostra, J; Garcia-Garcia, F; Yubero, F; Gonzalez-Elipe, AR
Solar Energy Materials and Solar Cells, 123 (2014) 130-138

ABSTRACT

This work reports the synthesis and the characterization of amorphous CoxSiyOz thin films prepared by magnetron sputtering from a single cathode. Porous layers with outstanding electrochromic properties are obtained at room temperature in one step by performing the deposition at a glancing angle configuration. The electrochromic behavior of these layers in a basic aqueous medium was dependent on the Co/Si ratio in the films and in all cases was characterized by a fast response, a high coloration efficiency and a complete reversibility after several hundred cycles. A characteristic feature of these electrochromic layers is that, for a similar thickness, the range of transmittance modulation can be tuned by changing the Co/Si ratio in the films and, specifically for films with a high concentration of silicon, to change their aspect from an almost transparent to a full colored state.


Abril, 2014 | DOI: 10.1016/j.solmat.2013.12.020

Mechanisms of Electron Transport and Recombination in ZnO Nanostructures for Dye-Sensitized Solar Cells


Vega-Poot, AG; Macias-Montero, M; Idigoras, J; Borras, A; Barranco, A; Gonzalez-Elipe, AR; Lizama-Tzec, FI; Oskam, G; Anta, JA
Chemphyschem, 15 (2014) 1088-1097

ABSTRACT

ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes.


Abril, 2014 | DOI: 10.1002/cphc.201301068

Perovskite Solar Cells Based on Nanocolumnar PlasmaDeposited ZnO Thin Films


Ramos, FJ; Lopez-Santos, MC; Guillen, E; Nazeeruddin, MK; Gratzel, M; Gonzalez-Elipe, AR; Ahmad, S
Chemphyschem, 15 (2014) 1148-1153

ABSTRACT

ZnO thin films having a nanocolumnar microstructure are grown by plasma-enhanced chemical vapor deposition at 423 K on pre-treated fluorine-doped tin oxide (FTO) substrates. The films consist of c-axis-oriented wurtzite ZnO nanocolumns with well-defined microstructure and crystallinity. By sensitizing CH3NH3PbI3 on these photoanodes a power conversion of 4.8 % is obtained for solid-state solar cells. Poly(triarylamine) is found to be less effective when used as the hole-transport material, compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), while the higher annealing temperature of the perovskite leads to a better infiltration in the nanocolumnar structure and an enhancement of the cell efficiency.


Abril, 2014 | DOI: 10.1002/cphc.201301215

Detecting single-electron events in TEM using low-cost electronics and a silicon strip sensor


Gontard, LC; Moldovan, G; Carmona-Galn, R; Lin, C; Kirkland, AI
Microscopy, 63(2) (2014) 119-130

ABSTRACT

There is great interest in developing novel position-sensitive direct detectors for transmission electron microscopy (TEM) that do not rely in the conversion of electrons into photons. Direct imaging improves contrast and efficiency and allows the operation of the microscope at lower energies and at lower doses without loss in resolution, which is especially important for studying soft materials and biological samples. We investigate the feasibility of employing a silicon strip detector as an imaging detector for TEM. This device, routinely used in high-energy particle physics, can detect small variations in electric current associated with the impact of a single charged particle. The main advantages of using this type of sensor for direct imaging in TEM are its intrinsic radiation hardness and large detection area. Here, we detail design, simulation, fabrication and tests in a TEM of the front-end electronics developed using low-cost discrete components and discuss the limitations and applications of this technology for TEM.


Abril, 2014 | DOI: 10.1093/jmicro/dft051

Long-term high temperature oxidation of CrAl(Y)N coatings in steam atmosphere


Mato, S; Alcala, G; Brizuela, M; Galindo, RE; Perez, FJ; Sanchez-Lopez, JC
Corrosion Science, 80 (2014) 453-460

ABSTRACT

The oxidation resistance of CrAl(Y)N coatings deposited by reactive magnetron sputtering on P92 steel substrates was tested at 650 °C in 100% steam atmosphere up to 2000 h of oxidation. Mass gain measurements and characterisation of coatings and scales after oxidation show the enhanced oxidation resistance provided by the coatings with respect to that of the substrate. The dominant influence of the film microstructure developed due to the presence of an adhesion interlayer of CrN at the coating/substrate interface over Y additions is evidenced. The best performance is achieved by a CrAlN dense coating of around 6 μm without adhesion interlayer.


Marzo, 2014 | DOI: 10.1016/j.corsci.2013.11.066

Osteoblasts Interaction with PLGA Membranes Functionalized with Titanium Film Nanolayer by PECVD. In vitro Assessment of Surface Influence on Cell Adhesion during Initial Cell to Material Interaction


Terriza, A; Vilches-Perez, JI; Gonzalez-Caballero, JL; de la Orden, E; Yubero, F; Barranco, A; Gonzalez-Elipe, AR; Vilches, J; Salido, M
Materials, 7(3) (2014) 1687-1708

ABSTRACT

New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material intended to be used for clinical purposes. For this purpose, we have developed in vitro studies on normal human osteoblasts (HOB®) HOB® osteoblasts grown on a resorbable Poly (lactide-co-glycolide) (PLGA) membrane foil functionalized by a very thin film (around 15 nm) of TiO2 (i.e., TiO2/PLGA membranes), designed to be used as barrier membrane. To avoid any alteration of the membranes, the titanium films were deposited at room temperature in one step by plasma enhanced chemical vapour deposition. Characterization of the functionalized membranes proved that the thin titanium layer completely covers the PLGA foils that remains practically unmodified in their interior after the deposition process and stands the standard sterilization protocols. Both morphological changes and cytoskeletal reorganization, together with the focal adhesion development observed in HOB osteoblasts, significantly related to TiO2 treated PLGA in which the Ti deposition method described has revealed to be a valuable tool to increase bioactivity of PLGA membranes, by combining cell nanotopography cues with the incorporation of bioactive factors.


Marzo, 2014 | DOI: 10.3390/ma7031687

c- C4F8 Plasmas for the Deposition of Fluorinated Carbon Films


Terriza, A; Macias-Montero, M; Lopez-Santos, MC; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 11 (2014) 289-299

ABSTRACT

Highly fluorinated polymeric (CFX), fluorine containing diamond-like carbon (F-DLC) and, for comparison, diamond-like carbon (DLC) films have been plasma deposited in a RF parallel plate reactor by using c-C4F8 as fluorine precursor and different mixtures of argon, C2H2, and H2. Plasmas have been characterized by optical emission spectroscopy, mass spectrometry, and Langmuir probe measurements. Differences in the film composition and structure have been related with the type of species formed in the plasma and with the self-bias potential developed at the deposition electrode. Additional experiments using CF4 have confirmed that the formation in the plasmas of neutral or ionized CxFy species with x > 2 is a critical factor for the synthesis of fluorine rich films.


Marzo, 2014 | DOI: 10.1002/ppap.201300129

Mechanical and phase stability of TiBC coatings up to 1000 degrees C


Abad, MD; Veldhuis, SC; Endrino, JL; Beake, BD; Garcia-Luis, A; Brizuela, M; Sanchez-Lopez, JC
Journal of Vacuum Science & Technology A, 32 (2014) 021508

ABSTRACT

TiBC coatings with different phase compositions (nanocrystalline TiBxCy or TiB2 phases mixed or not with amorphous carbon, a-C) were prepared by magnetron sputtering. These coatings were comparatively studied in terms of phase stability after thermal annealing at 250, 500, 750, and 1000 °C in argon using Raman and x-ray absorption near-edge spectroscopy techniques. The main differences were observed at temperatures above 500 °C when oxidation processes occur and the mechanical properties deteriorate. At 1000 °C, the samples were fully oxidized forming a-C, TiO2, and B2O3 as final products. Higher hardness and reduced indentation modulus values and better tribological properties were observed at 750 °C for nanocomposite structures including amorphous carbon and ternary TiBxCy phases. This behavior is attributed to a protective effect associated with the a-C phase which is achieved by the encapsulation of the nanocrystals in the coating and the better hard/lubricant phase ratio associated with this type of coating.


Marzo, 2014 | DOI: 10.1116/1.4861365

Low Temperature Production of Formaldehyde from Carbon Dioxide and Ethane by Plasma-Assisted Catalysis in a Ferroelectrically Moderated Dielectric Barrier Discharge Reactor


Gomez-Ramirez, A; Rico, VJ; Cotrino, J; Gonzalez-Elipe, A; Lambert, RM
ACS Catalysis, 4 (2014) 402-408

ABSTRACT

Plasma-assisted catalysis of the reaction between CO2 and C2H6 in a single-pass, ferroelectrically moderated dielectric barrier discharge reactor has been studied at near ambient temperature as a function of physicochemical and electrical reaction variables. The presence of small amounts of a vanadia/alumina catalyst dispersed on the BaTiO3 ferroelectric markedly enhanced the production of formaldehyde, the focus of this work. A maximum HCOH selectivity of 11.4% (defined with respect to the number of ethane carbon atoms consumed) at 100% ethane conversion was achieved, the other products being CO, H2O, H2, CH4 and a small amount of C3H8. N2O was also an effective partial oxidant (HCOH selectivity 8.9%) whereas use of O2 led to complete combustion, behavior that may be rationalized in terms of the electron impact excitation cross sections of the three oxidants. Control experiments with the coproducts CH4 and C3H8 showed that these species were not intermediates in HCOH formation from C2H6. Analysis of reactor performance as a function of discharge characteristics revealed that formaldehyde formation was strongly favored at low frequencies where the zero-current fraction of the duty cycle was greatest, the implication being that plasma processes also acted to destroy previously formed products. A tentative reaction mechanism is proposed that accounts for the broad features of formaldehyde production.


Febrero, 2014 | DOI: 10.1021/cs4008528

Plasma Deposition of Superhydrophobic Ag@ TiO2 Core@ shell Nanorods on Processable Substrates


Macias-Montero, M; Borras, A; Romero-Gomez, P; Cotrino, J; Frutos, F; Gonzalez-Elipe, AR
Plasma Process and Polymers, 11 (2014) 164-174

ABSTRACT

This work reports the low temperature plasma formation of Ag@TiO2 nanorods (NRs) on processable substrates. The layers have been analyzed by electron microscopy and secondary ion mass spectroscopy. The NRs morphologies suggest that the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining their shape, dimensions, and tilting orientation. Both amorphous and anatase Ag@TiO2 NRs surfaces are superhydrophobic, and turn into superhydrophilic by irradiation with UV light. This wetting behavior is discussed by considering the water penetration in the inter-NR space during the light-mediated transformation.


Febrero, 2014 | DOI: 10.1002/ppap.201300112

A Nanoscale Characterization with Electron Microscopy of Multilayered CrAlYN Coatings: A Singular Functional Nanostructure


Rojas, TC; Dominguez-Meister, S; Brizuela, M; Garcia-Luis, A; Fernandez, A; Sanchez-Lopez, JC
Microscoy and Microanalysis, 20 (2014) 14-24

ABSTRACT

A combination of transmission electron microscopy techniques and spatially resolved microanalysis is used to investigate the nanostructure, constituting phases, and chemical elemental distribution in CrAlYN multilayered coatings. The location of the metallic elements and their chemical state are needed to understand their functional properties. Samples were prepared with variable Al (4-12 at%) and Y (2-5 at%) contents by direct current reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N-2 mixtures under different deposition parameters (power applied to the target and rotation speed of the sample holder). The changes produced in the nanostructure and chemical distribution were investigated. Nanoscale resolution electron microscopy analysis has shown that these coatings present a singular nanostructure formed by multilayers containing at a certain periodicity nanovoids filled with molecular nitrogen. Spatially resolved energy dispersive spectroscopy and electron energy loss elemental mappings and profiles showed that the chromium, aluminum, and yttrium atoms are distributed in a sequential way following the position of the targets inside the deposition chamber. Analysis of the different atomic distribution and phases formed at the nanoscale is discussed depending on the deposition parameters.


Febrero, 2014 | DOI: 10.1017/S1431927613013962

Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres


Perez, FJ; Castaneda, SI; Hierro, MP; Galindo, RE; Sanchez-Lopez, JC; Mato, S
Oxidation of Metals, 81 (2014) 227-236

ABSTRACT

For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.


Febrero, 2014 | DOI: 10.1007/s11085-013-9447-2

Anchoring effect on (tetra)carboxyphenyl porphyrin/TiO2 composite films for VOC optical detection


Roales, J; Pedrosa, JM; Cano, M; Guillen, MG; Lopes-Costa, T; Castillero, P; Barranco, A; Gonzalez-Elipe, AR
RSC Advances, 4 (2014) 1974-1981

ABSTRACT

The optical gas sensing properties of Zn-(II)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP) and Zn-(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP) bound to microcolumnar TiO2 thin films have been compared and explained in terms of their different molecular structure and anchoring to the titania surface. This different binding has been confirmed by specular reflectance FTIR revealing that m-ZnTCPP is bound by its four carboxylic groups in contrast to p-ZnTCPP where two or three of these groups remain unanchored. As a consequence, the Soret band of the para derivative is blue shifted with respect to the solution, indicating H aggregation, while m-ZnTCPP remained in its monomeric form due to the planar anchoring by the four COOH groups to the titania matrix that would avoid porphyrin aggregation. The sensing performance of the two systems has been assessed by analyzing the spectral changes in their UV-visible spectra under exposure to six volatile organic compounds. Although the highly porous and non-dispersive TiO2 matrix allow good sensing ability in both cases, the response of the m-ZnTCPP/TiO2 composite has been found to be more intense and faster than that of p-ZnTCPP. Moreover, the use of identification patterns also indicates that the meta derivative achieves a more selective recognition of the selected analytes. This improvement in the sensing capabilities of m-ZnTCPP has been attributed to the absence of aggregation between adjacent macrocycles.


Enero, 2014 | DOI: 10.1039/C3RA42443J

On the kinetic and thermodynamic electron temperatures in non-thermal plasmas


Alvarez, R; Cotrino, J; Palmero, A
EPL (Europhysic Letters), 105 (2014)

ABSTRACT

The framework to describe the out-of-equilibrium free electrons in cold plasmas is developed assuming the electron entropy is defined through the Boltzmann H-theorem. Our theory explains why the Saha-Boltzmann relation among higher-lying excited states by means of the electron kinetic temperature is fulfilled, even when free electrons are far from equilibrium. The thermodynamic electron temperature, pressure and chemical potential have been introduced through the derivatives of the electron entropy. It is demonstrated that under usual conditions in cold plasmas, e.g. when the electron distribution function possesses the Maxwellian, Druyvestein or Kappa functional forms, kinetic and thermodynamic electron temperatures yield the same value.


Enero, 2014 | DOI: 10.1209/0295-5075/105/15001

Tribological behaviour at high temperature of hard CrAlN coatings doped with Y or Zr


Sanchez-Lopez, JC; Contreras, A; Dominguez-Meister, S; Garcia-Luis, A; Brizuela, M
Thin Solid Films, 550 (2014) 413-420

ABSTRACT

The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, 500 and 650 °C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.


Enero, 2014 | DOI: 10.1016/j.tsf.2013.10.041

Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers


Jimenez-Pique, E; Gonzalez-Garcia, L; Rico, VJ; Gonzalez-Elipe, AR
Thin Solid Films, 550 (2014) 444-449

ABSTRACT

This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained by focused ion beam and of the deformed areas. Zig-zagged layers present lower values of hardness and Young's modulus due to the collapse of the angles of the columns, but at the same time this configuration impedes the appearance of fracture or delamination, as observed for tilted columns.


Enero, 2014 | DOI: 10.1016/j.tsf.2013.10.022



2013


Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications


Macias-Montero, M; Filippin, AN; Saghi, Z; Aparicio, FJ; Barranco, A; Espinos, JP; Frutos, F; Gonzalez-Elipe, AR; Borras, A
Advanced Functional Materiales, 23 (2013) 5981-5989

ABSTRACT

A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO2) layer is presented. The developed procedure is a two-steps vacuum methodology involving the formation of supported single crystal small-molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single-crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.


Diciembre, 2013 | DOI: 10.1002/adfm.201301120

A single-source route to bulk samples of C3N and the co-evolution of graphitic carbon microspheres


King, TC; Matthews, PD; Holgado, JP; Jefferson, DA; Lambert, RM; Alavi, A; Wright, DS
Carbon, 64 (2013) 6-10

ABSTRACT

The thermolysis of commercially available m-phenylenediamine (1,3-(NH2)2C6H4) at 800 °C under a static vacuum in a sealed quartz tube provides the first bulk synthesis of C3N, whose properties have only been predicted theoretically previously. Hollow carbon microspheres (CMSs) which do not contain significant nitrogen doping (1–3 μm diameter) are co-produced in the reaction and readily separated from the C3N flakes. The separate C3N flakes and CMSs have been characterized by electron microscopy, X-ray spectroscopy and X-ray diffraction. These studies show that the samples of C3N and CMSs both possess multi-layered turbostratic graphitic structures. A new mechanism for the template-free assembly of CMSs is proposed on the basis of electron microscopy that involves bubble evolution from a static carbonized layer.


Noviembre, 2013 | DOI: 10.1016/j.carbon.2013.04.043

Synthesis and tribological properties of WSex films prepared by magnetron sputtering


Dominguez-Meister, S; Justo, A; Sanchez-Lopez, JC
Materials Chemistry and Physics, 142 (2013) 186-194

ABSTRACT

WSex films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe2 target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N2) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10−7 mm3 Nm−1) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSex hexagonal structure. The existence of a WSe2 rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSex, the formation of gradient composition from metallic W (hard) to WSe2 (lubricant) and carbon incorporation.


Octubre, 2013 | DOI: 10.1016/j.matchemphys.2013.07.004

Mechanosynthesis of nanocrystalline ZrB2-based powders by mechanically induced self-sustaining reaction method


Jalaly, M; Bafghi, MS; Tamizifar, M; Gotor, FJ
Advances in Applied Ceramics, 112 (2013) 383-388

ABSTRACT

Preparation of nanocrystalline ZrB2-based powder by aluminothermic and magnesiothermic reductions in M/ZrO2/B2O3 (M=Al or Mg) systems was investigated. In this research, high energy ball milling was employed to persuade necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). The course of MSR reactions were recorded by a noticeable pressure rise in the system during milling. Ignition times for ZrB2 formation by aluminothermic and magnesiothermic reductions were found to be 13 and 6 min, respectively. Zirconium diboride formation mechanism in both systems was explained through the analysis of the relevant sub-reactions.


Octubre, 2013 | DOI: 10.1179/1743676113Y.0000000091

A low-temperature single-source route to an efficient broad-band cerium(III) photocatalyst using a bimetallic polyoxotitanium cage


Lv, YK; Yao, MM; Holgado, JP; Roth, T; Steiner, A; Gan, LH; Lambert, RM; Wright, DS
RSC Advances, 3 (2013) 13659-13662

ABSTRACT

Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti : Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.


Septiembre, 2013 | DOI: 10.1039/C3RA41524D

Enhanced reactivity and related optical changes of Ag nanoparticles on amorphous Al2O3 supports


Pelaez, RJ; Castelo, A; Afonso, CN; Borras, A; Espinos, JP; Riedel, S; Leiderer, P; Boneberg, J
Nanotechnology, 24 (2013) 365702

ABSTRACT

Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al2O3) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al2O3 appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al2O3 samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al2O3 supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.


Septiembre, 2013 | DOI: 10.1088/0957-4484/24/36/365702

Atomistic model of ultra-smooth amorphous thin film growth by low-energy ion-assisted physical vapour deposition


Alvarez, R; Vazquez, L; Gago, R; Redondo-Cubero, A; Cotrino, J; Palmero, A
Journal of Physics D: Applied Physics, 46 (2013) 395303

ABSTRACT

The growth of ultra-smooth amorphous thin films induced by low-energy (below 1 keV) ion-assistance processes is studied. The relative contribution of ion-induced smoothening effects is analysed by means of a Monte Carlo model and experimental data. In general, highly rough granular or ultra-smooth (with roughness below one monolayer) films are produced depending on the competition between surface shadowing and ion-induced adatom mobility and sputtering. The ultra-smooth growth regime is experimentally and theoretically consistent with the Edwards–Wilkinson growth mode, which is related to the ion-induced enhancement of surface mobility. Overall, the framework and the fundamentals to analyse this type of growth are developed and discussed.


Septiembre, 2013 | DOI: 10.1088/0022-3727/46/39/395303

Enhancement of visible light-induced surface photo-activity of nanostructured N–TiO2 thin films modified by ion implantation


Romero-Gomez, P; Lopez-Santos, C; Borras, A; Espinos, JP; Palmero, A; Gonzalez-Elipe, AR
Chemical Physics Letters, 582 (2013) 95-99

ABSTRACT

This work reports the morphological and chemical modifications induced in TiO2 thin films by bombardment with high energy N+ ions at different temperatures and their different photo-activity responses after implantation under visible and UV light illumination. When implanted samples are illuminated with visible light, no dye photo-decolouration takes place despite that light transformed the surfaces from hydrophobic to hydrophilic. In agreement with the Wenzel model of wetting, correlation is found between visible light photo-activity and film morphology. We conclude that the photo-activity response can be separated into shallow and Schottky barrier photo-activity, this latter involving a thicker layer of material.


Septiembre, 2013 | DOI: 10.1016/j.cplett.2013.07.025

Low refractive index SiOF thin films prepared by reactive magnetron sputtering


Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Gonzalez, JC; Cotrino, J; Frutos, F; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F
Thin Solid Films, 542 (2013) 332-337

ABSTRACT

We have studied low refractive index fluorine doped silica thin films prepared by reactive magnetron sputtering. Two experimental parameters were varied to increase the porosity of the films, the geometry of the deposition process (i.e., the use of glancing angle deposition) and the presence of chemical etching agents (fluorine species) at the plasma discharge during film growth. The microstructure, chemistry, optical properties, and porosity of the films have been characterized by scanning electron and atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis, and spectroscopic ellipsometry. It is found that either the deposition at glancing angles or the incorporation of CFx species in the plasma discharge during film growth produces a decrease in the refractive index of the deposited films. The combined effect of the two experimental approaches further enhances the porosity of the films. Finally, the films prepared in a glancing geometry exhibit negative uniaxial birefringence.


Septiembre, 2013 | DOI: 10.1016/j.tsf.2013.07.009

Tuning of Cell–Biomaterial Anchorage for Tissue Regeneration


Leal-Egana, Aldo; Diaz-Cuenca, Aranzazu; Boccaccini, Aldo R
Advanced Materials, 25 (2013) 4049-4057

ABSTRACT

Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell–material anchorage? What are the currently investigated strategies to modify cell–matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell–matrix anchorage is discussed.


Agosto, 2013 | DOI: 10.1002/adma.201301227

Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy


Knappett, BR; Abdulkin, P; Ringe, E; Jefferson, DA; Lozano-Perez, S; Rojas, TC; Fernandez, A; Wheatley, AEH
Nanoscale, 5 (2013) 5765-5772

ABSTRACT

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.


Julio, 2013 | DOI: 10.1039/C3NR33789H

Liquids Analysis with Optofluidic Bragg Microcavities


Oliva-Ramirez, M; Gonzalez-Garcia, L; Parra-Barranco, J; Yubero, F; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 5 (2013) 6743-650

ABSTRACT

Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.


Julio, 2013 | DOI: 10.1021/am401685r

A new bottom-up methodology to produce silicon layers with a closed porosity nanostructure and reduced refractive index


Godinho, V; Caballero-Hernandez, J; Jamon, D; Rojas, TC; Schierholz, R; Garcia-Lopez, J; Ferrer, FJ; Fernandez, A
Nanotechnology, 24 (2013) 275604

ABSTRACT

A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50–150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n500 nm = 3.75) in comparison to dense coatings (n500 nm = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.


Julio, 2013 | DOI: 10.1088/0957-4484/24/27/275604

Preparation and characterization of CrO2 films by Low Pressure Chemical Vapor Deposition from CrO3


Aguilera, C; Gonzalez, JC; Borras, A; Margineda, D; Gonzalez, JM; Gonzalez-Elipe, AR; Espinos, JP
Thin Solid Films, 539 (2013) 1-11

ABSTRACT

Highly oriented CrO2 thin films have been heteroepitaxially grown on TiO2 rutile (110), (100) and (001) single crystalline substrates, by Low Pressure Chemical Vapor Deposition from CrO3 as precursor and flowing oxygen as carrier gas, under a pressure of 67 Pa. The experimental conditions were fine tuned by depositing on polycrystalline Ti foils, to improve the purity of the films and the deposition rate. A maximum deposition rate of 175 nm h− 1 was obtained.

The composition and texture of films, up to 2 μm thick, have been determined by X-ray diffraction (XRD) and Micro Raman, while their microstructure has been examined by Scanning Electron Microcopy and Atomic Force Microscopy, and their magnetic behavior has been tested by superconducting quantum interference device magnetometry. These techniques reveal that the phase purity, texture, microstructure and thickness of these films are dependent on the crystalline face of the rutile substrate and the deposition temperature. Thus, microscopy techniques, XRD and Raman spectroscopy confirm that highly textured CrO2 films were always obtained on the three rutile substrate faces when deposition temperature ranges between 616 K and 636 K. But these techniques also show that CrO2 films are unpurified with inclusions or patches of Cr2O3, for the most of the substrates and especially at high deposition temperatures. Magnetic measurements conclusively demonstrate that pure CrO2 films are only obtained when TiO2 (110) is used as a substrate.


Julio, 2013 | DOI: 10.1016/j.tsf.2013.04.118

Exploring the benefits of depositing hard TiN thin films by non-reactive magnetron sputtering


Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Applied Surface Science, 275 (2013) 121-126

ABSTRACT

The aim of this paper is to compare the mechanical and tribological properties of TiN coatings prepared in a conventional magnetron sputtering chamber according to two different routes: the usual reactive sputtering of a Ti target in an Ar/N2 atmosphere vs. the comparatively more simple sputtering of a TiN target in a pure Ar atmosphere. Improved properties in term of hardness and wear rates were obtained for films prepared by non-reactive sputtering route, due to the lower presence of oxynitride species and larger crystalline domain size. Additionally, a significant hardness enhancement (up to 45 GPa) is obtained when a −100 V d.c. bias is applied during growth. This behaviour is explained by non-columnar growth and small grain size induced by effective ion bombarding. These results demonstrate that non-reactive sputtering of TiN target appears a simple and efficient method to prepare hard wear-resistant TiN films.


Junio, 2013 | DOI: 10.1016/j.apsusc.2013.01.098

Structure and tribological properties of MoCN-Ag coatings in the temperature range of 25–700 °C


Shtansky, DV; Bondarev, AV; Kiryukhantsev-Korneev, PV; Rojas, TC; Godinho, V; Fernandez, A
Applied Surface Science, 273 (2013) 408-414

ABSTRACT

The preparation of hard coatings with low friction coefficient over a wide temperature range is still a challenge for the tribological community. The development of new nanocomposite materials consisting of different metal-ceramic phases, each of which exhibiting self-lubricating characteristics at different temperatures, may help to solve this problem. We report on the structure and tribological properties of MoCN-Ag coatings deposited by magnetron co-sputtering of Mo and C (graphite) targets and simultaneous sputtering of an Ag target either in pure nitrogen or in a gaseous mixture of Ar + N2. The structure and elemental composition of the coatings were studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, Raman spectroscopy, and glow discharge optical emission spectroscopy. The tribological properties of the coatings against an Al2O3 ball were investigated first at discrete temperatures of 25, 500, and 700 °C, and then during continuous heating in the temperature range of 25–700 °C. The coating structure and their respective wear tracks were also examined to elucidate their phase transformations during heat treatments. The lowest friction coefficients (<0.4) were observed in the temperature ranges of 25–100 °C and 400–700 °C and can be explained by the presence of a free amorphous carbon phase, which served as a lubricant at low temperatures, and by a positive role of silver and two phases forming at elevated temperatures, molybdenum oxide and silver molybdate, which provided lubrication above 400 °C. In the temperature range between 100 and 400 °C, the friction coefficient was relatively high. This problem is to be addressed in future works.


Mayo, 2013 | DOI: 10.1016/j.apsusc.2013.02.055

Combined reactive magnetron sputtering and plasma decomposition of non-volatile precursors to grow luminescent thin films


Gil-Rostra, J; Yubero, F; Ferrer, FJ; Gonzalez-Elipe, AR
Surface and Coatings Technology, 222 (2013) 144-150

ABSTRACT

This paper reports a new procedure of the preparation of mixed oxide thin films that combines the traditional reactive magnetron sputtering deposition with the plasma activated decomposition of non-volatile precursors sublimated by means of an effusion cell. The possibilities of this new experimental procedure are illustrated with the preparation of luminescent thin films consisting of rare earth (RE) cations (Tb3 +, Eu3 +) incorporated in an oxide matrix (TiO2 and SiO2). The oxide matrix component was supplied by reactive magnetron sputtering from metallic Ti or Si targets, while the RE cation was dosed by sublimation of acetylacetonate compounds of the selected elements. The obtained mixed oxide thin films have been fully characterized by different methods and their luminescent properties studied as a function of the matrix type and concentration of the RE element present in the film. The advantages of the synthesis procedure are highlighted with regard to its versatility and the possibility of tailoring the properties of complex luminescent materials.


Mayo, 2013 | DOI: 10.1016/j.surfcoat.2013.02.016

Tuning Dichroic Plasmon Resonance Modes of Gold Nanoparticles in Optical Thin Films


Gonzalez-Garcia, L; Parra-Barranco, J; Sanchez-Valencia, JR; Ferrer, J; Garcia-Gutierrez, MC; Barranco, A; Gonzalez-Elipe, AR
Advanced Functional Materials, 23 (2013) 1655-1663

ABSTRACT

A simple method is presented to tune the gold surface plasmon resonance (SPR) modes by growing anisotropic nanoparticles into transparent SiO2 thin films prepared by glancing angle deposition. In this type of composite film, the anisotropy of the gold nanoparticles, proved by gracing incidence small angle X-ray scattering, is determined by the tilted nanocolumnar structure of the SiO2 host and yields a strong film dichroism evidenced by a change from an intense colored to a nearly transparent aspect depending on light polarization and/or sample orientation. The formation in these films of lithographic non-dichroic SPR patterns by nanosecond laser writing demonstrates the potentialities of this procedure to develop novel optical encryption or anti-counterfeiting structures either at micrometer- or macroscales.


Abril, 2013 | DOI: 10.1002/adfm.201201900

Light induced hydrophilicity and osteoblast adhesion promotion on amorphous TiO2


Terriza, A; Diaz-Cuenca, A; Yubero, F; Barranco, A; Gonzalez-Elipe, AR; Caballero, JLG; Vilches, J; Salido, M
Journal of Biomedical Materials Research A, 101A (2013) 1026-1035

ABSTRACT

We have studied the effect of the UV induced superhydrophilic wetting of TiO2 thin films on the osteoblasts cell adhesion and cytoskeletal organization on its surface. To assess any effect of the photo-catalytic removal of adventitious carbon as a factor for the enhancement of the osteoblast development, 100 nm amorphous TiO2 thin layers were deposited on polyethylene terephthalate (PET), a substrate well known for its poor adhesion and limited wettability and biocompatibility. The TiO2/PET materials were characterized by X-ray photoelectron spectroscopy, and atomic force microscopy and their wetting behavior under light illumination studied by the sessile drop method. The amorphous TiO2 thin films showed a very poor photo-catalytic activity even if becoming superhydrophilic after illumination. The illuminated samples recovered partially its initial hydrophobic state only after their storage in the dark for more than 20 days. Osteoblasts (HOB) were seeded both on bare PET and on TiO2/PET samples immediately after illumination and also after four weeks storage in darkness. Cell attachment was much more efficient on the immediately illuminated TiO2/PET samples, with development of focal adhesions and cell traction forces. Although we cannot completely discard some photo-catalytic carbon removal as a factor contributing to this cell enhanced attachment, our photodegradation experiments on amorphous TiO2 are conclusive to dismiss this effect as the major cause for this behavior. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.


Abril, 2013 | DOI: 10.1002/jbm.a.34405

Differences in n-type doping efficiency between Al- and Ga-ZnO films


Gabas, M; Landa-Canovas, A; Costa-Kramer, JL; Agullo-Rueda, F; Gonzalez-Elipe, AR; Diaz-Carrasco, P; Hernandez-Moro, J; Lorite, I; Herrero, P; Castillero, P; Barranco, A; Ramos-Barrado, JR
Journal of Applied Physics, 113 (2013) 163709 (9 pages)

ABSTRACT

A careful and wide comparison between Al and Ga as substitutional dopants in the ZnO wurtzite structure is presented. Both cations behave as n-type dopants and their inclusion improves the optical and electrical properties of the ZnO matrix, making it more transparent in the visible range and rising up its electrical conductivity. However, the same dopant/Zn ratio leads to a very different doping efficiency when comparing Al and Ga, being the Ga cation a more effective dopant of the ZnO film. The measured differences between Al- and Ga-doped films are explained with the hypothesis that different quantities of these dopant cations are able to enter substitutionally in the ZnO matrix. Ga cations seem to behave as perfect substitutional dopants, while Al cation might occupy either substitutional or interstitial sites. Moreover, the subsequent charge balance after doping appear to be related with the formation of different intrinsic defects that depends on the dopant cation. The knowledge of the doped-ZnO films microstructure is a crucial step to optimize the deposition of transparent conducting electrodes for solar cells, displays, and other photoelectronic devices.


Abril, 2013 | DOI: 10.1063/1.4803063

Growth of SiO2 and TiO2 thin films deposited by reactive magnetron sputtering and PECVD by the incorporation of non-directional deposition fluxes


Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Gonzalez-Elipe, AR; Palmero, A
Physica Status Solidi (a), 210 (2013) 796-801

ABSTRACT

We have deposited TiO2 and SiO2 thin films by techniques as different as plasma-enhanced chemical vapor deposition (PECVD) and reactive magnetron sputtering under experimental conditions where highly directional deposition fluxes are avoided. The results indicate that whatever the deposition technique employed or even the precursor gas in the PECVD technique, films share common microstructural features: a mounded surface topography and a columnar arrangement in the bulk, with the column width growing linearly with film thickness. With the help of a Monte Carlo model of the deposition, we conclude that these common aspects are explained by solely taking into consideration the incorporation of a low-energy, isotropically directed, deposition flux onto a substrate at low temperature and under a weak plasma/surface interaction environment.


Abril, 2013 | DOI: 10.1002/pssa.201228656

Competing Misfit Relaxation Mechanisms in Epitaxial Correlated Oxides


Sandiumenge, F; Santiso, J; Balcells, L; Konstantinovic, Z; Roqueta, J; Pomar, A; Espinos, JP; Martinez, B
Physical Review Letters, 110 (2013) 107206

ABSTRACT

Strain engineering of functional properties in epitaxial thin films of strongly correlated oxides exhibiting octahedral-framework structures is hindered by the lack of adequate misfit relaxation models. Here we present unreported experimental evidence of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, and octahedral tilting energies in La0.7Sr0.3MnO3 epitaxial thin films grown on SrTiO3 substrates. Electronic softening of the Mn-O bonds near the substrate leads to the formation of an interfacial layer clamped to the substrate with strongly degraded magnetotransport properties, i.e., the so-called dead layer, while rigid octahedral tilts become relevant at advanced growth stages without significant effects on charge transport and magnetic ordering.


Marzo, 2013 | DOI: 10.1103/PhysRevLett.110.107206

Colored and Transparent Oxide Thin Films Prepared by Magnetron Sputtering: The Glass Blower Approach


Gil-Rostra, J; Chaboy, J; Yubero, F; Vilajoana, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 5 (2013) 1967-1976

ABSTRACT

This work describes the reactive magnetron sputtering processing at room temperature of several mixed oxide MxSiyOz thin films (M: Fe, Ni, Co, Mo, W, Cu) intended for optical, coloring, and aesthetic applications. Specific colors can be selected by adjusting the plasma gas composition and the Si–M ratio in the magnetron target. The microstructure and chemistry of the films are characterized by a large variety of techniques including X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and infrared spectroscopy, while their optical properties are characterized by UV–vis transmission and reflection analysis. Particularly, XAS analysis of the M cations in the amorphous thin films has provided valuable information about their chemical state and local structure. It is concluded that the M cations are randomly distributed within the SiO2 matrix and that both the M concentration and its chemical state are the key parameters to control the final color of the films.


Marzo, 2013 | DOI: 10.1021/am302778h

Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations


Garcia-Negrete, C. A.; Blasco, J.; Volland, M.; Rojas, T. C.; Hampel, M.; Lapresta-Fernandez, A.; Jimenez de Haro, M. C.; Soto, M.; Fernandez, A.
Environmental Pollution, 174 (2013) 134-141

ABSTRACT

The degree of aggregation and/or coalescence of Au-citrate nanoparticles (AuNPs, mean size 21.5 ± 2.9 nm), after delivery in simulated seawater, are shown to be concentration-dependent. At low concentrations no coalescence and only limited aggregation of primary particles were found. Experiments were performed in which the marine bivalve (Ruditapes philippinarum) was exposed to AuNPs or dissolved Au and subsequently, bivalve tissues were studied by Scanning and Transmission Electron Microscopy and chemical analyses. We show that the bivalve accumulates gold in both cases within either the digestive gland or gill tissues, in different concentrations (including values of predicted environmental relevance). After 28 days of exposure, electron-dense deposits (corresponding to AuNPs, as proven by X-ray microanalysis) were observed in the heterolysosomes of the digestive gland cells. Although non-measurable solubility of AuNPs in seawater was found, evidence is presented of the toxicity produced by Au3+ dissolved species (chloroauric acid solutions) and its relevance is discussed.


Marzo, 2013 | DOI: 10.1016/j.envpol.2012.11.014

Solvent-Controlled Synthesis and Luminescence Properties of Uniform Eu:YVO4 Nanophosphors with Different Morphologies


Nunez, N; Sabek, J; Garcia-Sevillano, J; Cantelar, E; Escudero, A; Ocañaa, M
European Journal of Inorganic Chemistry, 8 (2013) 1301-1309

ABSTRACT

A facile solvothermal route has been developed for the preparation of tetragonal europium-doped yttrium orthovanadate nanoparticles (Eu:YVO4) and is based on a homogeneous precipitation reaction at 120 °C from solutions of rare earth precursors (yttrium acetylacetonate and europium nitrate) and sodium orthovanadate in ethylene glycol or ethylene glycol/water mixtures. The nature of the solvent has a dramatic effect on the morphology and crystallinity of the resulting nanoparticles. Polycrystalline nanoellipsoids (130 × 60 nm) were obtained in pure ethylene glycol, whereas quasispherical nanoparticles (100 nm) with monocrystalline character precipitated in ethylene glycol/water (7:3 by volume) mixtures. To explain these different morphological and structural features, the mechanism of particles formation was investigated. The effects of the doping level on the luminescence properties (emission spectra and luminescence lifetime) were also evaluated to find the optimum nanophosphors. Finally, it is shown that the luminescent efficiency of the quasispherical nanoparticles was higher than that of the nanoellipsoids; this can be related to differences in crystallinity and in impurity content.


Marzo, 2013 | DOI: 10.1002/ejic.201201016

The distribution of elements in sequentially prepared MgB2 on SiC buffered Si substrate and possible pinning mechanisms


S. Chromik; A. Nishida; V. Strbik; M. Gregor; J.P. Espinós; J. Liday; R. Durny
Applied Surface Science, 269 (2013) 29-32

ABSTRACT

MgB2 thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg–B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15 nm and 50 nm) of stoichiometric MgB2 final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film.

X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15 nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of TC of the film to 20 K. We register different slope of the HC2(T)HC2(T) dependence – the lowest temperature value of HC2HC2 for the 15 nm thick film exceeds the one for the 50 nm thick film in spite of lower TC. We suppose that δl pinning mechanism is dominant for the 15 nm thick film.


Marzo, 2013 | DOI: 10.1016/j.apsusc.2012.10.019

Growth of silver on ZnO and SnO2 thin films intended for low emissivity applications


Alvarez, R; Gonzalez, JC; Espinos, JP; Gonzalez-Elipe, AR; Cueva, A; Villuendas, F
Applied Surface Science, 268 (2013) 507-515

ABSTRACT

In the present work we have investigated the relationships existing between the optical properties and the growth mechanism, microstructure and surface roughness of SnO2 and ZnO oxide films prepared by magnetron sputtering under conditions resembling those utilized in industry. Thin films of these oxides with different thicknesses were characterized by atomic force microscopy, glancing incidence X-ray diffraction (GIXRD), X-ray reflectometry and spectroscopic ellipsometry. The roughness evolution of the film properties (density, surface roughness and refraction index) as a function of their thickness has been evaluated within the concepts of the Dynamic Scaling Theory of thin film growth. Zinc oxide films were rougher than tin oxide films of similar thickness, indicating a different growing mechanism for the two materials. Silver was evaporated onto the surface of the two oxide thin films and its earlier stages of nucleation studied by background analysis of the X-ray photoemission spectra. A different nucleation mechanism was found depending on the nature of the oxide acting as substrate. The superior performance of the zinc oxide based low emissive coatings is related with a better wetting of silver on the surface of this oxide despite the comparatively lower roughness of the tin oxide layers.


Marzo, 2013 | DOI: 10.1016/j.apsusc.2012.12.156

Laser induced enhancement of dichroism in supported silver nanoparticles deposited by evaporation at glancing angles


Filippin, AN; Borras, A; Rico, VJ; Frutos, F; Gonzalez-Elipe, AR
Nanotechnology, 24 (2013) 045301

ABSTRACT

Silver nanoparticles (NPs) depicting well defined surface plasmon resonance (SPR) absorption were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV–vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the 'as-prepared' samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0° and 90°. Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed.


Febrero, 2013 | DOI: 10.1088/0957-4484/24/4/045301

Growth regimes of porous gold thin films deposited by magnetron sputtering at oblique incidence: from compact to columnar microstructures


Alvarez, R; Garcia-Martin, JM; Macias-Montero, M; Gonzalez-Garcia, L; Gonzalez, JC; Rico, V; Perlich, J; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 24 (2013) 045604

ABSTRACT

Growth regimes of gold thin films deposited by magnetron sputtering at oblique angles and low temperatures are studied from both theoretical and experimental points of view. Thin films were deposited in a broad range of experimental conditions by varying the substrate tilt angle and background pressure, and were analyzed by field emission scanning electron microscopy and grazing-incidence small-angle x-ray scattering techniques. Results indicate that the morphological features of the films strongly depend on the experimental conditions, but can be categorized within four generic microstructures, each of them defined by a different bulk geometrical pattern, pore percolation depth and connectivity. With the help of a growth model, a microstructure phase diagram has been constructed where the main features of the films are depicted as a function of experimentally controllable quantities, finding a good agreement with the experimental results in all the studied cases.


Febrero, 2013 | DOI: 10.1088/0957-4484/24/4/045604

Effects of plasma surface treatments of diamond-like carbon and polymeric substrata on the cellular behavior of human fibroblasts


Lopez-Santos, C; Fernandez-Gutierrez, M; Yubero, F; Vazquez-Lasa, B; Cotrino, J; Gonzalez-Elipe, A; San Roman, J
Journal of Biomaterials Applications, 27 (2013) 669-683

ABSTRACT

Surface properties play an important role in the functioning of a biomaterial in the biological environment. This work describes the influence of the changes that occurred on diamond-like carbon (DLC) and polymeric substrata by different nitrogen and ammonia plasmas treatments and its effects on the cell proliferation on these materials. All substrata were additionally subjected to the effect of neutral beams of nitrogen atoms and NH species for comparison purposes. Results about the proliferation, viability, and morphology of fibroblasts were correlated with surface chemical composition, surface tension, and topography. It was found that the presence of amine groups on the surface and the surface tension are beneficial factors for the cell growth. Surface roughness in DLC also plays a positive role in favoring cell adhesion and proliferation, but it can be detrimental for some of the treated polymers because of the accumulation of low molecular weight fragments formed as a result of the plasma treatments. Analysis of the overall results for each type of material allowed to define a unique parameter called ‘factor of merit’ accounting for the influence of the different surface characteristics on the cell deployment, which can be used to predict qualitatively the efficiency for cell growth.


Febrero, 2013 | DOI: 10.1177/0885328211422832

Valence band electronic structure characterization of the rutile TiO2 (110)-(1 x 2) reconstructed surface


Sanchez-Sanchez, C; Garnier, MG; Aebi, P; Blanco-Rey, M; de Andres, PL; Martin-Gago, JA; Lopez, MF
Surface Science, 608 (2013) 92-96

ABSTRACT

The electronic structure of the TiO2 (110)-(1 × 2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high symmetry surface directions, [001] and [1–10], has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the [001] direction located at about 7 eV below the Fermi level is reported. The existence of two different contributions in the emission from the defects-related state located in the gap of the surface is univocally shown for the first time.


Febrero, 2013 | DOI: 10.1016/j.susc.2012.09.019

Strong quantum confinement effects in SnS nanocrystals produced by ultrasound-assisted method


Azizian-Kalandaragh, Y; Khodayari, A; Zeng, ZP; Garoufalis, CS; Baskoutas, S; Gontard, LC
Journal of Nanoparticle Research, 15 (2013) 1388

ABSTRACT

Nanocrystalline SnS powder has been prepared using tin chloride (SnCl2) as a tin ion source and sodium sulfide (Na2S) as a sulfur ion source with the help of ultrasound irradiation at room temperature. The as-synthesized SnS nanoparticles were quantitatively analyzed and characterized in terms of their morphological, structural, and optical properties. The detailed structural and optical properties confirmed the orthorhombic SnS structure and a strongly blue shifted direct band gap (1.74 eV), for synthesized nanoparticles. The measured band gap energy of SnS nanoparticles is in a fairly good agreement with the results of theoretical calculations of exciton energy based on the potential morphing method in the Hartree–Fock approximation.


Enero, 2013 | DOI: 10.1007/s11051-012-1388-1

Small Pt nanoparticles on the TiO2 (110)–(1 × 2) surface


Sanchez-Sanchez, C; Martin-Gago, JA; Lopez, MF
Surface Science, 607 (2013) 159-163

ABSTRACT

Scanning tunnelling microscopy (STM) has been used to study the initial stages of Pt deposition on the TiO2 (110)–(1 × 2) surface. Experimental STM images recorded for Pt coverage of 0.1 and 0.4 ML, suggest a Volmer-Weber growth. For low coverage and RT deposition, small clusters homogeneously distributed on the surface terraces are observed. However, after annealing at 825 K, material agglomeration, with nucleation mainly at the cross-links, is observed as a consequence of Pt diffusion on the surface. Finally, the structure of small clusters has been determined, in good agreement with previous theoretical calculations.


Enero, 2013 | DOI: 10.1016/j.susc.2012.08.028

Tribological properties of surface-modified Pd nanoparticles for electrical contacts


Abad, MD; Sanchez-Lopez, JC
Wear, 297 (2013) 943-951

ABSTRACT

A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2 wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20 N, 1.82 GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1 kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well.


Enero, 2013 | DOI: 10.1016/j.wear.2012.11.009

Electrochromism in WOx and WxSiyOz Thin Films Prepared by Magnetron Sputtering at Glancing Angles


Garcia-Garcia, FJ; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Nanoscience and Nanotechnology Letters, 5 (2013) 89-93

ABSTRACT

This work reports the electrochromic evaluation of WxSiyOz and WOx glad thin films deposited by reactive magnetron sputtering at glancing angle. Their electrochemical properties were assessed by the analysis of cyclic voltammetry and chronoamperometry measurements in 0.1 M HClO4, whereas their optical properties were determined by studying their transmission and absorption spectra under operation conditions. Both types of thin films presented outstanding electrochromic properties characterized by a fast response, a high coloration and a complete reversibility after more than one thousand cycles.


Enero, 2013 | DOI: 10.1166/nnl.2013.1449



2012


Nanoporous silica microparticle interaction with toll-like receptor agonists in macrophages


Cejudo-Guillen, M; Ramiro-Gutierrez, M L; Labrador-Garrido, A; Diaz-Cuenca, A; Pozo, D
Acta Biomaterialia, 8 (2012) 4295-4303

ABSTRACT

Nanoporous silica microparticles (NSiO2-MP) are considered to be potential drug delivery systems and scaffolding platforms in tissue engineering. However, few biocompatibility studies regarding NSiO2-MP interaction with the immune system have been reported. Toll-like receptors (TLR) are involved in host defence as well as autoimmune and inflammatory diseases. The results show that NSiO2-MP up to 100 μg ml−1 do not affect macrophage cell viability after 24 h cell culture. Moreover, NSiO2-MP do not compromise the cell viability of TLR-activated Raw 264.7 cells, for either cell surface TLR (TLR1/TLR2/TLR4/TLR6) or endocytic compartment TLR (TLR3/TLR7/TLR9). Furthermore, Raw 264.7 cells do not respond to NSiO2-MP exposure in terms of IL-6 or IL-10 secretion. NSiO2-MP co-treatment in the presence of TLR ligands does not impair or enhance the secretion of the pro-inflammatory cytokine IL-6 or the regulatory cytokine IL-10. Thus, NSiO2-MP do not affect macrophage polarization towards a pro-inflammatory or immunosuppressive status, representing added value in terms of biocompatibility compared with other SiO2-based micro- and nanoparticles.


Diciembre, 2012 | DOI: 10.1016/j.actbio.2012.07.026

XPS and AES analyses of cerium conversion coatings generated on AA5083 by thermal activation


Sanchez-Amaya, JM; Blanco, G; Garcia-Garcia, FJ; Bethencourt, M; Botana, FJ
Surface and Coatings Technology, 213 (2012) 105-116

ABSTRACT

This paper describes the deep analysis of cerium conversion coatings developed with thermal activation on AA5083 under optimum processing conditions. Scanning electron microscopy (SEM), electron dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed to study these layers. Ar+ sputtering was also employed to analyse the coatings' core. Although conversion coatings based on Ce salts have been widely characterised in the literature for different aluminium alloys, the coatings developed with thermal activation on Al–Mg alloys have not been previously investigated with these techniques. SEM/EDX studies have demonstrated the existence of a heterogeneous layer formed by a film of aluminium oxide/hydroxide on the matrix as well as a series of dispersed islands of cerium deposited on the cathodic intermetallics. These results have been further confirmed by means of XPS. The XPS and AES results revealed that the outer layer comprises a mixture coating of Ce3 + (70%) and Ce4 + (30%) compounds. Although only Ce3 + compounds were detected at the inner part of the coating, possible reduction of Ce(IV) to Ce(III) due to the Ar+ beam could not be discarded. Obtained results allowed authors to confirm that the cerium conversion coatings developed have a similar structure to those previously reported for other aluminium alloys.


Diciembre, 2012 | DOI:

New insights into the synergistic effect in bimetallic-boron catalysts for hydrogen generation: The Co–Ru–B system as a case study


Arzac, G. M.; Rojas, T. C.; Fernandez, A.
Applied Catalysis B-Environmental, 128 (2012) 39-47

ABSTRACT

Catalysed sodium borohydride hydrolysis is a high-potential method to produce hydrogen for portable applications. Co–B catalysts are the most chosen because they are easily prepared, cheap and efficient. The addition of small amounts of Ru produces a significant enhancement in catalytic activity.

In the present work a series of Co–Ru–B catalysts with variable Ru content was prepared, isolated and characterized. The comprehension of the synergistic effect was achieved trough the incorporation of the nanostructural dimension to the study of surface and bulk chemical states of the involved atoms along the series. It was found that up to 70% (of total metal) atomic content of Ru the catalysts can be considered isostructural to the single Co–B catalyst in the nanoscale. A structural transition occurs in the case of the pure Ru–B material to produce a boron deficient material with higher nanoparticle size. This structural transition together with Co segregation and Ru dispersion play a key role when explaining a [OH−] dependent effect.

The inexistence of borate layers in Ru rich catalysts is suggestive in the research for non deactivating catalysts.


Noviembre, 2012 | DOI: 10.1016/j.apcatb.2012.02.013

Selective Detection of Volatile Organic Compounds by Spectral Imaging of Porphyrin Derivatives Bound to TiO2 Porous Films


Roales, J; Pedrosa, JM; Castillero, P; Cano, M; Richardson, TH; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 4 (2012) 5147-5154

ABSTRACT

In this work, the carboxylic acid derivatives of a free-base porphyrin, 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin, and 10 of its metal derivatives (TCPPs) have been used for optical gas sensing. For this purpose, microstructured columnar TiO2 thin films prepared by GAPVD (glancing angle physical vapor deposition) have been used as host materials for the porphyrins as they are non–dispersive and porous, allowing their use for UV–visible spectroscopy and gas sensing. The chemical binding between the dye molecules and the TiO2 has been studied through infrared spectroscopy, and the obtained spectral changes have been found to be compatible with chelating and/or bidentate binding modes of the carboxylate groups on the TiO2 surface. When hosted in the film, the UV–visible spectra of the porphyrins featured a blue shift and broadening of the Soret band with respect to the solution, which has been attributed to the formation of π–π aggregates between porphyrin molecules. The composite porphyrin/TiO2 films obtained from each of the 11 porphyrins have been exposed to 12 different volatile organic compounds (VOCs), and their respective gas–sensitive properties have been analyzed as a function of the spectral changes in their Soret band region in the presence of the analytes. The set of composite films has shown high selectivity to the analyzed volatile compounds. For each analyte, an innovative way of showing the different responses has been developed. By means of this procedure, an imagelike recognition pattern has been obtained, which allows an easy identification of every compound. The kinetics of the exposure to several analytes showed a fast, reversible and reproducible response, with response times of a few seconds, which has been attributed to both the sensitivity of the porphyrins and the high porosity of the TiO2 films. Also, increasing concentrations of the analytes resulted in an increase in the magnitude of the response, indicating that the sensor behavior is also concentration-dependent.


Octubre, 2012 | DOI: 10.1021/am301069

Following the Wetting of One-Dimensional Photoactive Surfaces


Macias-Montero, M; Borras, A; Alvarez, R; Gonzalez-Elipe, AR
Langmuir, 28 (2012) 15047-15055

ABSTRACT

This article aims toward a full description of the wetting conversion from superhydrophobicity to superhydrophilicity under illumination with UV light of high-density ZnO nanorods surfaces by (i) following the evolution of the clusters and superstructures formed by the nanocarpet effect as a function of the water contact angle (WCA); (ii) characterization of the superhydrophobic and superhydrophilic states with an environmental scanning electron microscope (ESEM); and (iii) using the nanocarpet effect as a footprint of both local and apparent water contact angles. Thus, the main objective of the article is to provide a general vision of the wettability of 1D photoactive surfaces. In parallel, the nanocarpet (NC) formation by clustering of vertically aligned ZnO nanorods (NR) when water is dripped on their surface and then dried is studied for the first time by taking advantage of the possibility of tuning the surface water contact angle of the ZnO NR structure under UV preillumination. As a result, we demonstrate the feasibility of controlling the size and other morphological characteristics of the NCs. Moreover, a strong anisotropic wetting behavior, characterized by a Δθ = θ – θ = 30°, is shown on an asymmetrically aligned NC surface resulting from arrays of tilted NRs. The study of the condensation/evaporation of water on/from an as-prepared (superhydrophobic) or a preilluminated (superhydrophilic) NR surface examined by an environmental scanning electron microscope has evidenced the formation of supported water droplets with polygonal shapes in the first case and the complete filling of the inter-NR space in the latter. The long-term stability of the NC clusters has been utilized as a footprint to track the penetration depth of water within the inter-NR space in the three borderline regions of water droplets. This analysis has shown that for moderately hydrophobic surfaces (i.e., water contact angles lower than 130°) water droplets do not present a well-defined borderline trace but a spreading region where water penetrates differently with the NR interspace. The transition from a Cassie–Baxter to a modified Cassie–Baxter to finish in a Wenzel wetting state is found on these surfaces depending on the UV preillumination time and is explained with a model where water interaction with the NR units is the critical factor determining the macroscopic wetting behavior of these surfaces.


Octubre, 2012 | DOI: 10.1021/la3028918

Deactivation, reactivation and memory effect on Co–B catalyst for sodium borohydride hydrolysis operating in high conversion conditions


Arzac, GM; Hufschmidt, D; De Haro, MCJ; Fernandez, A; Sarmiento, B; Jimenez, MA; Jimenez, MM
International Journal of Hydrogen Energy, 37 (2012) 14373-14381

ABSTRACT

A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.


Octubre, 2012 | DOI: 10.1016/j.ijhydene.2012.06.117

DLC coatings for UHMWPE: Relationship between bacterial adherence and surface properties


Del Prado, G; Terriza, A; Ortiz-Perez, A; Molina-Manso, D; Mahillo, I; Yubero, F; Puertolas, JA; Manrubia-Cobo, M; Barrena, EG; Esteban, J
Journal of Biomedical Materials Research Part A, 100A (2012) 2813-2820

ABSTRACT

Development of intrinsically antibacterial surfaces is of key importance in the context of prostheses used in orthopedic surgery. This work presents a thorough study of several plasma-based coatings that may be used with this functionality: diamond-like carbon (DLC), fluorine-doped DLC (F-DLC), and a high-fluorine-content-carbon-fluor polymer (CFX). The coatings were obtained by a radio-frequency plasma-assisted deposition on ultra high molecular weight polyethylene (UHMWPE) samples and physicochemical properties of the coated surfaces were correlated with their antibacterial performance against collection and clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The fluorine content and the relative amount of CC and CF bonds were controlled by X-ray photoelectron spectroscopy, and hydrophobicity and surface tension by contact angle measurements. Surface roughness was studied by Atomic Force Microscopy. Additional nanoidentation studies were performed for DLC and F-DLC coatings. Unpaired t test and regression linear models evaluated the adherence of S. aureus and S. epidermidis on raw and coated UHMWPE samples. Comparing with UHMWPE, DLC/UHMWPE was the least adherent surface with independence of the bacterial species, finding significant reductions (p ≤ 0.001) for nine staphylococci strains. Bacterial adherence was also significantly reduced in F-DLC/ UHMWPE and CFx/UHMWPE for six strains. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:2813–2820, 2012.


Octubre, 2012 | DOI: 10.1002/jbm.a.34220

Chemical and microstructural characterization of (Y or Zr)-doped CrAlN coatings


Rojas, T. C.; El Mrabet, S.; Dominguez-Meister, S.; Brizuela, M.; Garcia-Luis, A.; Sanchez-Lopez, J. C.
Surface and Coatings Technology, 211 (2012) 104-110

ABSTRACT

Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlN-based coatings including Y or Zr as dopants (≈ 2 at.%) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N2 mixtures. The hardness properties are found in the range of 22–33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000 °C is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating.


Octubre, 2012 | DOI: 10.1016/j.surfcoat.2011.07.071

Critical thickness and nanoporosity of TiO2 optical thin films


Borras, A; Alvarez, R; Sanchez-Valencia, JR; Ferrer, J; Gonzalez-Elipe, AR
Microscopy and Microanalysis, 18 (2012) 1-9

ABSTRACT

This work reports on the porosity and refraction index of TiO2 thin films as a function of the film thickness. Samples were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a microwave electron cyclotron resonance (MW-ECR) reactor at room temperature using titanium tetra-isopropoxide (MP) as precursor. Experimental parameters such as plasma gas composition (pure oxygen and argon/oxygen mixtures) and pressure (either ECR conditions or "normal" pressure, i.e. 10(-4) or 10(-3) torrs correspondently) were varied. The evolution of the thin film microstructure, porosity and optical properties is critically studied by AFM, SEM, water adsorption isotherms, ellipsometry and UV-Vis transmittance and the existence of a certain critical thickness (t(c)) demonstrated. The porosity of the films with thicknesses ranging from several tens of nanometers up to half a micrometer is evaluated by QCM-isotherms at room temperature. The dependency of this critical thickness with the plasma conditions is evaluated experimental and theoretically. Thus, the microstructure change at t(c) is attributed to a transition from a surface diffused dominated growth mechanism for t < t(c) to another where shadowing is predominant. Dynamic scaling analysis of the two regimes and their Monte Carlo simulation complete the reported study.


Septiembre, 2012 | DOI: 10.1016/j.micromeso.2012.04.035

Phase composition and tribomechanical properties of Ti-B-C nanocomposite coatings prepared by magnetron sputtering


Sanchez-Lopez, JC; Abad, MD; Justo, A; Gago, R; Endrino, JL; Garcia-Luis, A; Brizuela, M
Journal of Physics D: Applied Physics, 45 (2012) 375401

ABSTRACT

Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio applied to the graphite and TiB2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB2-like structure to a distorted TiBxCy ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiBxCy phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiBxCy components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp2-bonded carbon phase associated with the diminution of the friction level.


Septiembre, 2012 | DOI: 10.1088/0022-3727/45/37/375401

Microstructural characterization of hydrophobic Ti1−xAlxN coatings with moth-eye-like surface morphology


Godinho, V; Lopez-Santos, C; Rojas, TC; Philippon, D; de Haro, MCJ; Lucas, S; Fernandez, A
Journal of Alloys and Compounds, 536 (2012) S398-S406

ABSTRACT

Ti1−xAlxN thin films with different Al content were deposited by magnetron sputtering. The combination of electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) was used to evaluate the composition of the coatings. The effect of Al content on the morphology and properties of the coatings was investigated. High resolution electron microscopy and related techniques revealed the formation of a pillared moth-eye-like nanostructure with variable size and distribution of meso- and nano-columns and different degree of open porosity that depends on the Al content on the coating. For low Al content (x ≤ 0.21) c-(Ti,Al)N highly porous columns ending in a sharp pyramidal shape present low reflectivity and high hydrophobicity. While the precipitation of h-AlN phase at the column boundaries for x = 0.71 suppresses the c-(Ti,Al)N columnar growth and produces a smother surface, with higher reflectivity and less hydrophobic character.


Septiembre, 2012 | DOI: 10.1016/j.jallcom.2012.02.178

Characterization of highly crosslinked polyethylenes by colorimetry


Martinez-Morlanes, MJ; Terriza, A; Yubero, F; Puertolas, JA
Polymer Testing, 31 (2012) 841-847

ABSTRACT

Colour analysis appears to be a robust technique for characterizing vitamin E doping and gamma irradiation of medical grade polyethylene samples. The analysis procedure described in this paper is of great interest because it can easily distinguish between polyethylene samples with differences in vitamin E (α-tocopherol) doping of about 0.1 wt% and gamma irradiation doses of 30 kGy. It is found that the colour differences (with respect to untreated samples) induced by gamma irradiation and/or vitamin E doping add-up linearly. This method for detecting the presence of vitamin E is fast, simple and non-destructive.


Septiembre, 2012 | DOI: 10.1016/j.polymertesting.2012.06.005

Wall slip phenomena in concentrated ionic liquid-based magnetorheological fluids


Gomez-Ramirez, A; Lopez-Lopez, MT; Gonzalez-Caballero, F; Duran, JDG
Rheologica Acta, 51 (2012) 793-803

ABSTRACT

Ionic liquids (ILs) have been recently proposed as carrier for magnetorheological (MR) fluids. Their special properties, such as very low vapor pressure and high thermal stability, make ILs highly suitable dispersion media to increase the broad range of technological applications that magnetorheological fluids already have. It has been just reported that using ILs as carriers in MR fluids an improvement in the colloidal stability and suspension redispersibility is obtained. In this work, the magnetorheological behavior of highly concentrated suspensions in ILs is studied. Two kinds of suspensions were analyzed: using an ionic liquid of low conductivity and a mineral oil as carriers. In both cases, silica-coated iron microparticles were used as solid phase, being the solid volume concentration of 50% vol. A complete magnetorheological analysis focused on the wall slip phenomenon was performed. Steady-state and oscillatory experiments were carried out. In order to study wall slip effects, all experiments were performed with a plate-plate system, using both smooth and rough measuring surfaces. A significant effect of wall slip was observed when the experiments were performed using smooth surfaces. The novelty of this paper is mainly based on (1) the use of an ionic liquid as carrier to prepare magnetic suspensions, and (2) the analysis of wall slip phenomena in MR fluids with a particle content close to the maximum packing fraction.


Septiembre, 2012 | DOI: 10.1007/s00397-012-0639-5

Charge collection properties of dye-sensitized solar cells based on 1-dimensional TiO2 porous nanostructures and ionic-liquid electrolytes


Gonzalez-Garcia, Lola; Idigoras, Jesus; Gonzalez-Elipe, Agustin R.; Barranco, Angel; Anta, Juan A.
Journal of Photochemistry and Photobiology A-Chemistry, 241 (2012) 58-66

ABSTRACT

Dye solar cells consisting of mesoporous TiO 2 nanocolumnar films sensitized with a highly absorptive indoline dye were studied to estimate the charge collection efficiency provided by porous 1-dimensional (1-D) nanostructures in combination with viscous, fast-recombining electrolytes. The TiO 2 mesoporous nanostructured films were prepared by physical vapor deposition at glancing incidence (GLAD-PVD). Electrochemical Impedance Spectroscopy (EIS) in the dark was utilized to extract the transport and recombination properties of the fabricated devices. Due to their high porosity, the TiO 2 nanocolumnar electrodes incorporated a dye amount similar to that admitted by nanoparticulated electrodes with higher thickness. This fact, together with the longer lifetimes of electrons obtained for the GLAD-PVD electrodes, lead to an overall improvement of the charge collection and photovoltaic properties with respect to randomly packed electrodes. Measured diffusion lengths were improved by a factor between 2 and 3 with respect to the disordered nanostructure. The present results demonstrate the capability of partially ordered nanostructures to improve charge collection in devices constructed with fast-recombining electrolytes.


Agosto, 2012 | DOI: 10.1016/j.jphotochem.2012.05.015

Software package to calculate the effects of the core hole and surface excitations on XPS and AES


Tougaard, S; Yubero, F
Surface and Interface Analysis, 44 (2012) 1114-1118

ABSTRACT

We report on a new software package that allows to calculate the energy loss processes in a photo- and Auger electron spectrum. The calculations are performed within our previously published semiclassical dielectric response model. The model takes into account energy loss, which takes place because of the sudden creation of the static core hole and as the photoelectron travels in the bulk, passes the surface region and continues in the vacuum where it interacts with its image charge before it ends up in the electron spectrometer. It is a one-step model, which includes interference effects between these excitations. The only input in the calculations is the dielectric function of the material. We discuss the capabilities of the software and illustrate some examples of its practical application, including comparison with experimental spectra. We hope the software will be useful for the investigations of fundamental excitation mechanisms in XPS and AES. The software is free for noncommercial use.


Agosto, 2012 | DOI: 10.1002/sia.4855

The effect of nickel on alloy microstructure and electrochemical behaviour of AA1050 aluminium alloy in acid and alkaline solutions


Garcia-Garcia, FJ; Skeldon, P; Thompson, GE; Smith, GC
Electrochimica Acta, 75 (2012) 229-238

ABSTRACT

The study investigates the influence of nickel and magnesium additions to AA1050 aluminium alloy on the alloy electrochemical behaviour in sodium hydroxide and hydrochloric solutions under conditions relevant to industries that use alkaline etching as a standard surface treatment procedure and to the lithographic and electronic industries where surface convolution is assisted by pitting in hydrochloric acid. Scanning and transmission electron microscopes were used to characterize the intermetallic particles, and scanning Kelvin probe microscopy was utilised in monitoring the surface potential. Nickel is shown to be incorporated into second phase particles, which mostly consisted of Al3Fe and α-(AlFeSi) phases, resulting in enhanced cathodic activity on the aluminium surface. Consequently, the dissolution rates of the superpure aluminium, alloys without nickel addition and alloy with nickel addition are increased respectively in sodium hydroxide, and increased pitting is respectively promoted in hydrochloric acid. In contrast, the addition of magnesium to the alloy had negligible influence on the etching and pitting behaviour.


Julio, 2012 | DOI: 10.1016/j.electacta.2012.04.106

Weakly Interacting Molecular Layer of Spinning C60 Molecules on TiO2 (110) Surfaces


Sanchez-Sanchez, C; Lanzilotto, V; Gonzalez, C; Verdini, A; de Andres, PL; Floreano, L; Lopez, MF; Martin-Gago, JA
Chemistry-A European Journal, 18 (2012) 7382-7387

ABSTRACT

The adsorption of C60, a typical acceptor organic molecule, on a TiO2 (110) surface has been investigated by a multitechnique combination, including van der Waals density functional calculations. It is shown that the adsorbed molecules form a weakly interacting molecular layer, which sits on the fivefold-coordinated Ti that is confined between the prominent bridging oxygen rows (see figure).


Junio, 2012 | DOI: 10.1002/chem.201200627

Investigation of the growth mechanisms of a-CH x coatings deposited by pulsed reactive magnetron sputtering


Lopez-Santos, C; Colaux, JL; Gonzalez, JC; Lucas, S
Journal of Physical Chemistry C, 116 (2012) 12017-12026

ABSTRACT

The study of the growth mechanisms of amorphous hydrogenated carbon coatings (a-CH x) deposited by reactive pulsed magnetron discharge in Ar + C 2H 2, Ar + H 2, and Ar + C 2H 2 + H 2 low-pressure atmospheres is presented in this work. Hydrogen-containing species of the reactant gas affect the microstructure and surface properties of the a-CH x thin films. The dynamic scaling theory has been used to relate the main reactive species involved in the deposition process to the growth mechanisms of the thin film by means of the analysis of the roughness evolution. Anomalous scaling effects have been observed in smooth a-CH x coatings. Dynamic scaling exponents α, β, and z indicate a general growth controlled by surface diffusion mechanisms. Hydrogen species have an influence on the lateral growth of the a-CH x coatings and are involved in the development of a polymeric-like structure. Meanwhile, hydrocarbon species promote the generation of higher aggregates, which increases the roughness of a more sp 2 clustering structure of the a-CH x coating.


Junio, 2012 | DOI: 10.1021/jp300697s

Vertical and tilted Ag-NPs@ZnO nanorods by plasma-enhanced chemical vapour deposition


Macias-Montero, M; Borras, A; Saghi, Z; Espinos, JP; Barranco, A; Cotrino, J; Gonzalez-Elipe, AR
Nanotechnology, 23 (2012) 255303

ABSTRACT

Supported ZnO nanorods have been prepared at 405 K by plasma-enhanced chemical vapour deposition (PECVD) using diethylzinc as precursor, oxygen plasma and silver as the promotion layer. The nanorods are characterized by a hollow and porous microstructure where partially percolated silver nanoparticles are located. By changing different deposition parameters like the thickness of the silver layer, the type of oxidation pretreatment or the geometry of the deposition set-up, the length, the width and the tilting angle of the nanorods with respect to the substrate can be modified. Other nanostructures like nanobushes, zigzag linear structures and stacked bilayers with nanocolumns of TiO 2 can also be prepared by adjusting the deposition conditions. A phenomenological model relying on the assessment of the diverse nanostructure morphologies and the evidence provided by an in situ x-ray photoelectron spectroscopy (XPS) experiment has been proposed to describe their formation mechanism. From this analysis it is deduced that the effect of the electrical field of the plasma sheath, the high mobility of silver and silver oxide, and the diffusion of the precursor molecules are some of the critical factors that must converge by the formation of the nanorods.


Junio, 2012 | DOI: 10.1088/0957-4484/23/25/255303

Three-dimensional fabrication and characterisation of core-shell nano-columns using electron beam patterning of Ge-doped SiO2


Gontard, LC; Jinschek, JR; Ou, HY; Verbeeck, J; Dunin-Borkowski, RE
Applied Physics Letters, 100 (2012) 263113

ABSTRACT

A focused electron beam in a scanning transmission electron microscope (STEM) is used to create arrays of core-shell structures in a specimen of amorphous SiO2 doped with Ge. The same electron microscope is then used to measure the changes that occurred in the specimen in three dimensions using electron tomography. The results show that transformations in insulators that have been subjected to intense irradiation using charged particles can be studied directly in three dimensions. The fabricated structures include core-shell nano-columns, sputtered regions, voids, and clusters.


Junio, 2012 | DOI: 10.1063/1.4731765

Roughness assessment and wetting behavior of fluorocarbon surfaces


Terriza, A; Alvarez, R; Borras, A; Cotrino, J; Yubero, F; Gonzalez-Elipe, AR
Journal of Colloid and Interface Science, 376 (2012) 274-282

ABSTRACT

The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the influence of the surface chemical composition and surface roughness on the water advancing and receding contact angles. Diamond like carbon and two fluorocarbon materials with different fluorine content have been prepared by plasma enhanced chemical vapor deposition and characterized by X-ray photoemission, Raman and FT-IR spectroscopies. Very rough surfaces have been obtained by deposition of thin films of these materials on polymer substrates previously subjected to plasma etching to increase their roughness. A direct correlation has been found between roughness and water contact angles while a superhydrophobic behavior (i.e., water contact angles higher than 150° and relatively low adhesion energy) was found for the films with the highest fluorine content deposited on very rough substrates. A critical evaluation of the methods currently used to assess the roughness of these surfaces by atomic force microscopy (AFM) has evidenced that calculated RMS roughness values and actual surface areas are quite dependent on both the scale of observation and image resolution. A critical discussion is carried out about the application of the Wenzel model to account for the wetting behavior of this type of surfaces.


Junio, 2012 | DOI: 10.1016/j.jcis.2012.03.010

Microstructural and chemical characterization of nanostructured Tialsin coatings with nanoscale resolution


Godinho, V; Rojas, TC; Trasobares, S; Ferrer, FJ; Delplancke-Ogletree, MP; Fernandez, A
Microscopy and Microanalysis, 18 (2012) 568-581

ABSTRACT

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).


Junio, 2012 | DOI: 10.1017/S1431927612000384

Correlation lengths, porosity and water adsorption in TiO2 thin films prepared by glancing angle deposition


Gonzalez-Garcia, L; Parra-Barranco, J; Sanchez-Valencia, JR; Barranco, A; Borras, A; Gonzalez-Elipe, AR; Garcia-Gutierrez, MC; Hernandez, JJ; Rueda, DR; Ezquerra, TA
Nanotechnology, 23 (2012) 205701

ABSTRACT

This paper reports a thorough microstructural characterization of glancing angle deposited (GLAD) TiO 2 thin films. Atomic force microscopy (afm), grazing-incidence small-angle x-ray scattering (GISAXS) and water adsorption isotherms have been used to determine the evolution of porosity and the existence of some correlation distances between the nanocolumns constituting the basic elements of the films nanostructure. It is found that the deposition angle and, to a lesser extent, the film thickness are the most important parameters controlling properties of the thin film. The importance of porosity and some critical dimensions encountered in the investigated GLAD thin films is highlighted in relation to the analysis of their optical properties when utilized as antireflective coatings or as hosts and templates for the development of new composite materials.


Mayo, 2012 | DOI: 10.1088/0957-4484/23/20/205701

Tuning liver stiffness against tumours: An in vitro study using entrapped cells in tumour-like microcapsules


Leal-Egana, A; Fritsch, A; Heidebrecht, F; Diaz-Cuenca, A; Nowicki, M; Bader, A; Kas, J
Journal of the mechanical behavior of biomedical materials, 9 (2012) 113-121

ABSTRACT

Liver fibrosis is a reversible pathology characterized by the up-regulated secretion and deposition of ECM proteins and inhibitors of metalloproteinases, which increase the stiffness and viscosity of this organ. Since recent studies have shown that fibrosis preceded the generation of hepatocellular carcinomas, we hypothesize that liver fibrosis could play a role as a mechanism for restricting uncontrolled cell proliferation, inducing the mortality of cancer cells and subsequent development of primary tumours.

With this purpose, in this work we analysed in vitro how the modulation of stiffness can influence proliferation, viability and aggregation of hepatocarcinoma cells (HepG(2)) embedded in 3D micromilieus mimicking values of elasticity of fibrotic liver tissues.

Experiments were performed by immobilizing up to 10 HepG(2) cells within microcapsules made of 0.8%, 1.0% and 1.4% w/v alginate which, besides having values of elasticity from the lower-healthy to the upper-fibrotic range liver tissues, lacked domains for proteases, mimicking the micromilieu existing in hepatic primary tumours.

Our results show that entrapped cells exhibited a short duplication phase followed by an irreversible decay stage, in which cell mortality could be mediated by two mechanisms: mechanical stress, in the case of cells entrapped in a stiffer micromilieu; and mass transfer limitations produced by pore coarsening at the interface cell-matrix, in softer micromilieus.

According to the authors' knowledge, this work represents the first attempt to elucidate the role of liver fibrosis during Hepatocarcinoma pathologies, suggesting that the generation of a non-biodegradable and mechanically unfavourable environment surrounding cancer cells could control the proliferation, migration of metastatic cells and the subsequent development of primary tumours.


Mayo, 2012 | DOI: 10.1016/j.jmbbm.2012.01.013

Attenuation lengths of high energy photoelectrons in compact and mesoporous SiO2 films


Ferrer, FJ; Gil-Rostra, J; Gonzalez-Garcia, L; Rubio-Zuazo, J; Romero-Gomez, P; Lopez-Santos, MC; Yubero, F
Surface Science, 606 (2012) 820-824

ABSTRACT

We have experimentally evaluated attenuation lengths (AL) of photoelectrons traveling in compact and micro and mesoporous (∼ 45% voids) SiO 2 thin films with high (8.2-13.2 keV) kinetic energies. The films were grown on polished Si(100) wafers. ALs were deduced from the intensity ratio of the Si 1s signal from the SiO 2 film and Si substrate using the two-peaks overlayer method. We obtain ALs of 15-22 nm and 23-32 nm for the compact and porous SiO 2 films for the range of kinetic energies considered. The observed AL values follow a power law dependence on the kinetic energy of the electrons where the exponent takes the values 0.81 ± 0.13 and 0.72 ± 0.12 for compact and porous materials, respectively.


Mayo, 2012 | DOI: 10.1016/j.susc.2012.01.017

Self-assembly at room temperature of thermally stable discrete and extended oligomers of polycyclic aromatics on Ag(100): induced dipoles and cooperative effects


Papageorgiou, AC; Alavi, A; Lambert, RM
Chemical Communications, 48 (2012) 3394-3396

ABSTRACT

Thermally stable nanoarchitectures are realized on the Ag(100) surface by self-assembly of asymmetrically substituted arenes. The process is instigated by adsorption-induced molecule → surface charge transfer that gives rise to in-plane dipole moments. Observation and calculation indicate that cooperative interactions further enhance the stability of these polarizable systems.


Abril, 2012 | DOI: 10.1039/c2cc17728e

Plasma deposition of perylene-adamantane nanocomposite thin films for NO 2 room-temperature optical sensing


Aparicio, FJ; Blaszczyk-Lezak, I; Sanchez-Valencia, JR; Alcaire, M; Gonzalez, JC; Serra, C; Gonzalez-Elipe, AR; Barranco, A
Journal of Physical Chemistry C, 116 (2012) 8731-8740

ABSTRACT

This work reports the preparation, by a new remote assisted plasma deposition process, of luminescent nanocomposite thin films consisting of an insoluble organic matrix where photonically active perylene molecules are embedded. The films are obtained by the remote plasma deposition of adamantane and perylene precursor molecules. The results show that the adamantane precursor is very effective to improve the perylene–adamantane nanocomposite transparency in comparison with plasma deposited perylene films. The plasma deposited adamantane films have been characterized by secondary-ion mass spectrometry and FT-IR spectroscopy. These techniques and atomic force microscopy (AFM) have been also used for the characterization of the nanocomposite films. Their optical properties (UV–vis absorption, fluorescence, and refractive index) have been also determined and their sensing properties toward NO2 studied. It is found that samples with the perylene molecules embedded within the transparent plasma deposited matrix are highly sensitive toward this gas and that the sensitivity of the films can be adjusted by modifying the aggregation state of the perylene molecules, as determined by the analysis of their fluorescence spectra. By monitoring the fluorescence emission of these films, it has been possible to detect a NO2 concentration as low as 0.5 ppm in air at room temperature. Because of their chemical stability and transparency in the UV region, the remote plasma deposited adamantane thin films have revealed as an optimum host matrix for the development of photonically active composites for sensing applications.


Abril, 2012 | DOI: 10.1021/jp209272s

Influence of plasma-generated negative oxygen ion impingement on magnetron sputtered amorphous SiO2 thin films during growth at low temperatures


Macias-Montero, M; Garcia-Garcia, FJ; Alvarez, R; Gil-Rostra, J; Gonzalez, JC; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Applied Physics, 111 (2012) 054312 (6 pages)

ABSTRACT

Growth of amorphous SiO2 thin films deposited by reactive magnetron sputtering at low temperatures has been studied under different oxygen partial pressure conditions. Film microstructures varied from coalescent vertical column-like to homogeneous compact microstructures, possessing all similar refractive indexes. A discussion on the process responsible for the different microstructures is carried out focusing on the influence of (i) the surface shadowing mechanism, (ii) the positive ion impingement on the film, and (iii) the negative ion impingement. We conclude that only the trend followed by the latter and, in particular, the impingement of O- ions with kinetic energies between 20 and 200 eV, agrees with the resulting microstructural changes. Overall, it is also demonstrated that there are two main microstructuring regimes in the growth of amorphous SiO2 thin films by magnetron sputtering at low temperatures, controlled by the amount of O2 in the deposition reactor, which stem from the competition between surface shadowing and ion-induced adatom surface mobility.


Marzo, 2012 | DOI: 10.1063/1.3691950

Quantification of low levels of fluorine content in thin films


Ferrer, FJ; Gil-Rostra, J; Terriza, A; Rey, G; Jimenez, C; Garcia-Lopez, J; Yubero, F
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 274 (2012) 65-69

ABSTRACT

Fluorine quantification in thin film samples containing different amounts of fluorine atoms was accomplished by combining proton-Rutherford Backscattering Spectrometry (p-RBS) and proton induced gamma-ray emission (PIGE) using proton beams of 1550 and 2330 keV for p-RBS and PIGE measurements, respectively. The capabilities of the proposed quantification method are illustrated with examples of the analysis of a series of samples of fluorine-doped tin oxides, fluorinated silica, and fluorinated diamond-like carbon films. It is shown that this procedure allows the quantification of F contents as low as 1 at.% in thin films with thicknesses in the 100-400 nm range.


Marzo, 2012 | DOI: 10.1016/j.nimb.2011.11.042

Nanoecotoxicity effects of engineered silver and gold nanoparticles in aquatic organisms


Lapresta-Fernandez, A; Fernandez, A; Blasco, J
TrAC Trends in Analytical Chemistry, 32 (2012) 40-59

ABSTRACT

Engineered nanoparticles (ENPs) are increasingly being incorporated into commercial products. A better understanding is required of their environmental impacts in aquatic ecosystems.

This review deals with the ecotoxicity effects of silver and gold ENPs (AgNPs and AuNPs) in aquatic organisms, and considers the means by which these ENPs enter aquatic environments, their aggregation status and their toxicity. Since ENPs are transported horizontally and vertically in the water column, we discuss certain factors (e.g., salinity and the presence of natural organic materials), as they cause variations in the degree of aggregation, size range and ENP toxicity. We pay special attention to oxidative stress induced in organisms by ENPs.

We describe some of the main analytical methods used to determine reactive oxygen species, antioxidant enzyme activity, DNA damage, protein modifications, lipid peroxidation and relevant metabolic activities. We offer an overview of the mechanisms of action of AgNPs and AuNPs and the ways that relevant environmental factors can affect their speciation, agglomeration or aggregation, and ultimately their bio-availability to aquatic organisms.

Finally, we discuss similarities and differences in the adverse effects of ENPs in freshwater and salt-water systems.


Febrero, 2012 | DOI: 10.1016/j.trac.2011.09.007

Public concern over ecotoxicology risks from nanomaterials: Pressing need for research-based information


Lapresta-Fernandez, A; Fernandez, A; Blasco, J
Environment International, 39 (2012) 148-149

ABSTRACT

[No abstract available]


Febrero, 2012 | DOI: 10.1016/j.envint.2011.10.012

Electrochromic Behavior of WxSiyOz Thin Films Prepared by Reactive Magnetron Sputtering at Normal and Glancing Angles


Gil-Rostra, J; Cano, M; Pedrosa, JM; Ferrer, FJ; Garcia-Garcia, F; Yubero, F; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 4 (2012) 628-638

ABSTRACT

This work reports the synthesis at room temperature of transparent and colored WxSiyOz thin films by magnetron sputtering (MS) from a single cathode. The films were characterized by a large set of techniques including X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), Fourier transform infrared (FT-IR), and Raman spectroscopies. Their optical properties were determined by the analysis of the transmission and reflection spectra. It was found that both the relative amount of tungsten in the W–Si MS target and the ratio O2/Ar in the plasma gas were critical parameters to control the blue coloration of the films. The long-term stability of the color, attributed to the formation of a high concentration of W5+ and W4+ species, has been related with the formation of W–O–Si bond linkages in an amorphous network. At normal geometry (i.e., substrate surface parallel to the target) the films were rather compact, whereas they were very porous and had less tungsten content when deposited in a glancing angle configuration. In this case, they presented outstanding electrochromic properties characterized by a fast response, a high coloration, a complete reversibility after more than one thousand cycles and a relatively very low refractive index in the bleached state.


Febrero, 2012 | DOI: 10.1021/am2014629

Microwave-Assisted Synthesis and Luminescence of Mesoporous REDoped YPO4 (RE = Eu, Ce, Tb, and Ce plus Tb) Nanophosphors with Lenticular Shape


Rodriguez-Liviano, S; Aparicio, FJ; Rojas, TC; Hungria, AB; Chinchilla, LE; Ocana, M
Crystal Growth and Design, 12 (2012) 635-645

ABSTRACT

Mesoporous tetragonal RE:YPO 4 nanophosphors (RE = Eu, Ce, Tb, and Ce + Tb) with a lenticular morphology, narrow size distribution, and high surface area have been prepared by an homogeneous precipitation procedure consisting of aging, at low temperature (80-120 °C) in a microwave oven, ethylene glycol solutions containing only yttrium acetylacetonate and phosphoric acid. This synthesis method involves important advantages such as its simplicity, rapidness (reaction time = 7 min), and high reaction yields. The mechanism of nanoparticle growth has been also addressed finding that the lenticular nanoparticles are formed through an ordered aggregation of smaller entities, which explains their porosity. In all cases, the doping levels were systematically varied in order to optimize the nanophosphors luminescence. All optimum nanophosphors presented a high luminescence quantum yield (QY). In particular, for the Eu and Tb doped systems, the obtained QY values (60% for Eu and 80% for Tb) were the highest so far reported for this kind of nanomaterial. The morphological, microstructural, and luminescent properties of these nanophosphors and their dispersibility in water make them suitable for biomedical applications.


Febrero, 2012 | DOI: 10.1021/cg201358c

Magnetron sputtered a-SiO xN y thin films: A closed porous nanostructure with controlled optical and mechanical properties


Godinho, V; Rojas, TC; Fernandez, A
Microporous and Mesoporous Materials, 149 (2012) 142-146

ABSTRACT

Amorphous silicon oxynitride coatings with similar composition and different closed porosity were prepared by magnetron sputtering. Pores size, shape and distribution were evaluated by scanning electron microscopy and transmission electron microscopy. Raman and EELS analysis proved that the pores are filled with molecular nitrogen trapped during deposition. The mechanical properties evaluated by nanoindentation shows that the presence of closed nano-porosity does not compromise the mechanical integrity of these coatings. The introduction of closed porosity is shown as a good strategy for obtaining lower dielectric constant silicon oxynitride coatings with similar composition while keeping the good mechanical properties (∼13 GPa) characteristic of this type of coatings. The presence of close porosity gives also a good stability of coatings properties as compared to open porosity microstructures where gas phase in contact with the coatings can affect coatings properties.


Febrero, 2012 | DOI: 10.1016/j.micromeso.2011.08.018

An international round-robin calibration protocol for nanoindentation measurements


Cabibbo, M; Ricci, P; Cecchini, R; Rymuza, Z; Sullivan, J; Dub, S; Cohen, S
Micron, 43 (2012) 215-222

ABSTRACT

Nanoindentation has become a common technique for measuring the hardness and elastic–plastic properties of materials, including coatings and thin films. In recent years, different nanoindenter instruments have been commercialised and used for this purpose. Each instrument is equipped with its own analysis software for the derivation of the hardness and reduced Young's modulus from the raw data. These data are mostly analysed through the Oliver and Pharr method. In all cases, the calibration of compliance and area function is mandatory. The present work illustrates and describes a calibration procedure and an approach to raw data analysis carried out for six different nanoindentation instruments through several round-robin experiments. Three different indenters were used, Berkovich, cube corner, spherical, and three standardised reference samples were chosen, hard fused quartz, soft polycarbonate, and sapphire. It was clearly shown that the use of these common procedures consistently limited the hardness and reduced the Young's modulus data spread compared to the same measurements performed using instrument-specific procedures. The following recommendations for nanoindentation calibration must be followed: (a) use only sharp indenters, (b) set an upper cut-off value for the penetration depth below which measurements must be considered unreliable, (c) perform nanoindentation measurements with limited thermal drift, (d) ensure that the load–displacement curves are as smooth as possible, (e) perform stiffness measurements specific to each instrument/indenter couple, (f) use Fq and Sa as calibration reference samples for stiffness and area function determination, (g) use a function, rather than a single value, for the stiffness and (h) adopt a unique protocol and software for raw data analysis in order to limit the data spread related to the instruments (i.e. the level of drift or noise, defects of a given probe) and to make the H and Er data intercomparable.


Febrero, 2012 | DOI: 10.1016/j.micron.2011.07.016

Superhydrophobic supported Ag-NPs@ZnO-nanorods with photoactivity in the visible range


Macias-Montero, M; Borras, A; Saghi, Z; Romero-Gomez, P; Sanchez-Valencia, JR; Gonzalez, JC; Barranco, A; Midgley, P; Cotrino, J; Gonzalez-Elipe, AR
Journal of Materials Chemistry, 22 (2012) 1341-1346

ABSTRACT

In this article we present a new type of 1D nanostructures consisting of supported hollow ZnO nanorods (NRs) decorated with Ag nanoparticles (NPs). The 3D reconstruction by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) electron tomography reveals that the Ag NPs are distributed along the hollow interior of the ZnO NRs. Supported and vertically aligned Ag-NPs@ZnO-NRs grow at low temperature (135 °C) by plasma enhanced chemical vapour deposition on heterostructured substrates fabricated by sputtered deposition of silver on flat surfaces of Si wafers, quartz slides or ITO. The growth mechanisms of these structures and their wetting behavior before and after visible light irradiation are critically discussed. The as prepared surfaces are superhydrophobic with water contact angles higher than 150°. These surfaces turn into superhydrophilic with water contact angles lower than 10° after prolonged irradiation under both visible and UV light. The evolution rate of the wetting angle and its dependence on the light characteristics are related to the nanostructure and the presence of silver embedded within the ZnO NRs.


Enero, 2012 | DOI: 10.1039/C1JM13512K

Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)


Brandt, Katrin; Chiu, May E.; Watson, David J.; Tikhov, Mintcho S.; Lambert, Richard M.
Journal of Physical Chemistry C, 116 (2012) 4605-4611

ABSTRACT

The chemoselective hydrogenation of crotonaldehyde to crotyl alcohol was studied by temperature-programmed desorption/reaction, high-resolution XPS, and NEXAFS. The organic molecule adsorbed without decomposition, all three possible hydrogenation products were formed and desorbed, and the clean overall reaction led to no carbon deposition. Selectivities up to 95% were found under TPR conditions. The observed behavior corresponded well with selectivity trends previously reported for Ag/SiO2 catalysts, and the present findings permit a rationalization of the catalytic performance in terms of pronounced coverage-dependent changes in adsorption geometries of the reactant and the products. Thus, at low coverages, the C═O bond in crotonaldehyde lies almost parallel to the metal surface, whereas the C═C was appreciably tilted, favoring hydrogenation of the former and disfavoring hydrogenation of the latter. With increasing coverage of reactants, the C═C bond was forced almost parallel to the surface, rendering it vulnerable to hydrogenation, thus markedly decreasing selectivity toward formation of crotyl alcohol. Butanol formation was the result of an overall two-step process: crotonaldehyde → crotyl alcohol → butanol, further hydrogenation of the desired product crotyl alcohol being promoted at high hydrogen coverage due to the C═C bond in the unsaturated alcohol being driven from a tilted to a flat-lying geometry. Finally, an explanation is offered for the strikingly different behavior of Ag(111) and Cu(111) in the chemoselective hydrogenation of crotonaldehyde in terms of the different degrees of charge transfer from metal to C═O π bond, as suggested by C 1s XPS binding energies.


Enero, 2012 | DOI: 10.1021/jp208831h

Analysis and application of the theories that rationalize the crystalline structures of fluorite-related rare earth oxides


Lopez-Cartes, C; Perez-Omil, JA; Rodriguez-Izquierdo, JM; Calvino, JJ
Catalysis Today, 180 (2012) 161-180

ABSTRACT

The main current theories dealing with the crystalline structures of the fluorite related rare earth oxides, including those corresponding to reduced oxides, one based on the distribution of the coordination defect inside the fluorite structure, and the other which proposes the establishment of modular sequences constituted by modules with fluorite structure, are presented and comparatively explored in detail. Our in-depth analysis of both approximations indicates that they in fact provide smart and efficient rationalizations of the currently known intermediate rare earth oxides structures. We prove however that the strict application of the principles and rules proposed by each theory does not yield unique and unambiguous results for most of the members of the homologous series, as it has been claimed up to now. Moreover, the controversy about the reliability of these two, apparently different and competing, theories is definitely clarified and the exact equivalence of their structural predictions is demonstrated. Finally, we propose new extra systematization rules, not considered up to now in neither of these theoretical approaches, to overcome the observed limitations to properly rationalize the structure of this so technologically important family of oxides.


Enero, 2012 | DOI: 10.1016/j.cattod.2011.04.032

Aluminum incorporation in alpha-PbO2 type TiO2 at pressures up to 20 GPa


Escudero, A; Langenhorst, F
Physics of the Earth and Planetary Interiors, 190 (2012) 87-94

ABSTRACT

Aluminum incorporation into the high pressure polymorph of TiO2 with the structure of alpha-PbO2 has been studied from 10 to 20 GPa and 1300 degrees C by XRD, high-resolution Al-27 MAS-NMR and TEM. Al-doped alpha-PbO2 type TiO2 can be recovered at atmospheric pressure. Al2O3 solubility in alpha-PbO2 type TiO2 increases with increasing the synthesis pressure. The alpha-PbO2 type TiO2 polymorph is able to incorporate up to 35 wt.% Al2O3 at 13.6 GPa and 1300 degrees C, being the substitution of Ti4+ by Al3+ on normal octahedral sites and the formation of oxygen vacancies the mechanism of solubility. The transition to the higher pressure TiO2 polymorph with the ZrO2 baddeleyite structure, akaogiite, has not been observed in the quenched samples at room pressure. The microstructure of the recovered sample synthesized at 16 GPa and 1300 degrees C points to the existence of an intermediate non-quenchable aluminum titanium oxide phase at these conditions.


Enero, 2012 | DOI: 10.1016/j.pepi.2011.11.002

Nanoscale mechanically induced structural and electrical changes in Ge 2Sb 2Te 5 films


Cecchini, R; Benitez, JJ; Sanchez-Lopez, JC; Fernandez, A
Journal of Applied Physics, 111 (2012) 016101 (3 pages)

ABSTRACT

We demonstrate that the microstructure and electrical properties of Ge2Sb2Te5 films can be changed by a nanoscale mechanical process. Nanoscratching is used to define modified areas onto an as-deposited crystalline Ge2Sb2Te5 film. Scanning tunneling microscopy measurements show that the modified areas have a very low electrical conductivity. Micro-Raman measurements indicate that the mechanically induced microstructural changes are consistent with a phase transformation from crystalline to amorphous, which can be reversed by laser irradiation.


Enero, 2012 | DOI: 10.1063/1.3673592

Influence of silver content on the tribomechanical behavior on Ag-TiCN bioactive coatings


Sanchez-Lopez, JC; Abad, MD; Carvalho, I; Galindo, RE; Benito, N; Ribeiro, S; Henriques, M; Cavaleiro, A; Carvalho, S
Surface and Coatings Technology, 206 (2012) 2192-2198

ABSTRACT

Surface modification of bulk materials used in biomedical applications has become an important prerequisite for better biocompatibility. In particular, to overcome the particle generation, low-wear coatings based on carbon (nitrogen) and containing antimicrobial elements such as silver are promising candidates. Thus, the present work explores the potentialities of silver-containing carbonitride-based (Ag-TiCN) thin films prepared by direct current unbalanced reactive magnetron sputtering. The silver content in the coatings was varied from 0 to 26.7at.% by changing the targets and the fraction of C 2H 2 and N 2 in the gas mixture with Ar. The obtained Ag-TiCN based coatings were characterized in terms of composition and microstructure. Mechanical and tribological properties of the films were studied by nanoindentation and reciprocating pin-on disk testing in a fetal bovine serum solution, respectively. Raman, scanning electron microscope and energy dispersive X-ray analysis was carried out in the contact region after tribological tests to obtain information about the friction mechanism. The cytotoxicity of the coatings was assessed by in vitro tests using fibroblast cells. The coatings comprised a mixture of TiC xN 1-x, Ag and a-C(N) x phases whose relative proportion varied depending on the Ag/Ti ratio. The mechanical, tribological and cytotoxicity properties were correlated with the chemical and phase composition. When the Ag/Ti ratios were below 0.20 (Ag contents <6.3at.%) the films resulted harder (~18GPa) with higher wear resistance (~10 -6mm 3/Nm), showing similar friction coefficient (~0.3) and good biocompatibility.


Enero, 2012 | DOI: 10.1016/j.surfcoat.2011.09.059

Analysis of multifunctional titanium oxycarbide films as a function of oxygen addition


Chappe, JM; Fernandes, AC; Moura, C; Alves, E; Barradas, NP; Martin, N; Espinos, JP; Vaz, F
Surface and Coatings Technology, 206 (2012) 2525-2534

ABSTRACT

Reactive magnetron sputtering was used to deposit titanium oxycarbide thin films. The overall set of results showed that the oxygen flow rate, and thus the composition of the atmosphere in the deposition chamber, controls the composition of the titanium oxycarbide thin films obtained by reactive sputtering. Rutherford Backscattering Spectroscopy analysis revealed the existence of three major types of films, indexed to their particular composition ratios. A detailed study by X-ray photoelectron spectroscopy was carried out in order to characterize the evolution of the Tisingle bondC, Csingle bondO and Csingle bondC bonds induced by the increase of the oxygen partial pressure, which was found to be closely related with the different zones of composition that were suggested. Micro-Raman spectroscopy and X-ray diffraction measurements allowed describing the complex nature of the film structure, namely in what concerns different phases and their evolution, texture phenomena and grain size evolution as a function of the particular composition and film types (different zones). Electrical conductivity revealed a transition from a metallic to a semi-conducting behavior as a function of the oxygen concentration in the films, in good agreement with the different zones that were suggested. Similarly, optical properties supported this gradual change and for oxygen contents higher than 67 at.%, the films exhibited typical reflectance of insulator materials (interferences) in the UV, visible and near IR regions.


Enero, 2012 | DOI: 10.1016/j.surfcoat.2011.11.005

Microstructure, composition and P-T conditions of rutile from diamondiferous gneiss of the Saxonian Erzgebirge, Germany


Escudero, A; Miyajima, N; Langenhorst, F
Chemie der erde-geochemistry, 72 (2012) 25-30

ABSTRACT

The chemical composition and microstructure of rutile grains in a ultra-high pressure metamorphic gneiss of the Saxonian Erzgebirge, Germany have been studied by Raman spectroscopy, SEM, EMPA and TEM. Rutile inclusions in garnet contain free dislocations, iron-enriched dislocations and exsolved ilmenite lamellae, while subgrain boundaries are observed in rutile grains of the rock matrix. The previously reported alpha-PbO2 type TiO2 phase could not be confirmed by our TEM observations. On the basis of Zr solubility in the rutile and the presence of microdiamonds, minimum metamorphic peak conditions of 3.95 GPa and 915 degrees C are estimated.


Enero, 2012 | DOI: 10.1016/j.chemer.2011.11.001



2011


Soft plasma processing of organic nanowires: a route for the fabrication of 1D organic heterostructures and the template synthesis of inorganic 1D nanostructures


Maria Alcaire, Juan R. Sanchez-Valencia, Francisco J. Aparicio, Zineb Saghi, Juan C. Gonzalez-Gonzalez, Angel Barranco, Youssef Oulad Zian, Agustin R. Gonzalez-Elipe, Paul Midgley, Juan P. Espinos, Pierangelo Groening and Ana Borras
Nanoscale, 3 (2011) 4554-4559

ABSTRACT

Hierarchical (branched) and hybrid metal-NPs/organic supported NWs are fabricated through controlled plasma processing of metalloporphyrin, metallophthalocyanine and perylene nanowires. The procedure is also applied for the development of a general template route for the synthesis of supported metal and metal oxide nanowires.


Noviembre, 2011 | DOI: 10.1039/C1NR11001B

Comments on "an essay on contact angle measurements": Determination of surface roughness and modeling of the wetting behavior


Terriza, A; Alvarez, R; Yubero, F; Borras, A; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 8 (2011) 998-1002

ABSTRACT

This commentary addresses the problem of determining surface roughness values and their use to assess the wetting behavior of surfaces. For very rough surfaces it is shown that depending on the observation scale by atomic force microscopy (AFM) quite different RMS roughness values can be obtained and that only the values taken at saturation can be used for properly describing the roughness of the examined materials. This effect has clear consequences when trying to apply wetting models to account for the influence of roughness on contact angles. These ideas are discussed with examples taken from rough polymer surfaces subjected to plasma etching. Debate - Discussion: To account for the wetting behavior of real surfaces within the Wenzel and similar models only surface roughness values determined at saturation can be used. This implies to check different observation areas by AFM and to choose the RMS roughness values once a maximum value of this parameter has been reached.


Noviembre, 2011 | DOI: 10.1002/ppap.201100081

Electrical properties and applications of carbon based nanocomposite materials: An overview


Sanjinés, R., Abad, M.D., Vâju, C., Smajda, R., Mionić, M., Magrez, A.
Surface and Coatings Technology, 206 (2011) 727-733

ABSTRACT

The allotropic forms of carbon (amorphous and polycrystalline graphite, carbon black, fullerenes, nanotubes, graphene) exhibit a large variety of charge transport properties which have been stimulating fundamental and applied research for the development of new devices based on micro and nano-sized electronic systems. Carbon based nanocomposites offer the possibility to improve the device performances and to develop novel multifunctional material systems by combining the properties of each individual phase. In this paper we review the electrical properties of carbon materials and some of the most exciting carbon based nanocomposites, as well as their potential technological applications. First, the electrical properties of amorphous and polycrystalline graphitic materials and those of their related nanocomposites materials are discussed. Second, an overview of the state-of-art on research and applications of carbon nanotube-based composites is presented. Third, we discuss briefly the emerging area of research related to graphene materials. Finally, the electrical properties and applications of conducting carbon black aggregates and carbon black/polymer composites are overviewed.


Noviembre, 2011 | DOI: 10.1016/j.surfcoat.2011.01.025

Enhanced gas sensing performance of TiO2 functionalized magneto-optical SPR sensors


M.G. Manera, G. Montagna, E. Ferreiro-Vila, L. González-García, J.R. Sánchez-Valencia, A.R. González-Elipe, A.Cebollada, J.M. Garcia-Martin, A. Garcia-Martin, G. Armelles and R. Rella
Journal of Materials Chemistry, 21 (2011) 16049-16056

ABSTRACT

Porous TiO2 thin films deposited by glancing angle deposition are used as sensing layers to monitor their sensing capabilities towards Volatile Organic Compounds both in a standard Surface Plasmon Resonance (SPR) sensor and in Magneto-Optical Surface Plasmon Resonance (MO-SPR) configuration in order to compare their sensing performances. Here our results on the enhanced sensing capability of these TiO2 functionalized MO-SPR sensors with Au/Co/Au transducers with respect to traditional SPR gas sensors are presented.


Octubre, 2011 | DOI: 10.1039/c1jm11937k

Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing


Lapresta-Fernández, A., Doussineau, T., Dutz, S., Steiniger, F., Moro, A.J., Mohr, G.J.
Nanotechnology, 22 (2011), Article number 415501

ABSTRACT

This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (&#8764;10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (&#8764;3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.


Octubre, 2011 | DOI: 10.1088/0957-4484/22/41/415501

Aligned TiO(2) nanocolumnar layers prepared by PVD-GLAD for transparent dye sensitized solar cells


Gonzalez-Garcia, L; Gonzalez-Valls, I; Lira-Cantu, M; Barranco, A; Gonzalez-Elipe, AR
Energy and Environmental Science, 4 (2011) 3426-3435

ABSTRACT

Transparent thin film electrodes made of vertically aligned nanocolumns of TiO2 with well-controlled oblique angles were grown by physical vapor deposition at glancing incidence (PVD-GLAD). For an electrode thickness of 500 nm, we report a 40% variation on solar cell efficiency (from 0.6% to 1.04%) when the deposition angle was modified between 60° and 85°. Transparent thicker films with higher surface area deposited at the optimal angle of 70° were grown with a zigzag morphology which confers high mechanical strength to the thin films. Using this topology, the application of an electrode thickness of 3 m in a DSC resulted in a power conversion efficiency of 2.78% maintaining electrode transparency.


Septiembre, 2011 | DOI: 10.1039/C0EE00489H

Theoretical and experimental characterization of TiO2 thin films deposited at oblique angles


Álvarez, R., González-García, L., Romero-Gómez, P., Rico, V., Cotrino, J., Gonzalez-Elipe, A.R., Palmero, A.
Journal of Physics D: Applied Physics, 44 (2011) Article number 385302

ABSTRACT

The microstructural features of amorphous TiO2 thin films grown by the electron beam physical vapour deposition technique at oblique angles have been experimentally and theoretically studied. The microstructural features of the deposited films were characterized by considering both the column tilt angle and the increase in the column thickness with height. A Monte Carlo model of film growth has been developed that takes into account surface shadowing, short-range interaction between the deposition species and the film surface, as well as the angular broadening of the deposition flux when arriving at the substrate. The good match between simulations and experimental results indicates the importance of these factors in the growth and microstructural development of thin films deposited at oblique angles.


Septiembre, 2011 | DOI: 10.1088/0022-3727/44/38/385302

Colored semi-transparent Cu-Si oxide thin films prepared by magnetron sputtering


Gil-Rosta, J; Yubero, F; Fernandez, R; Vilajoana, T; Artus, P; Dursteler, JC; Cotrino, J; Ortega, I; Gonzalez-Elipe, AR
Optical Material Express, 1 (2011) 1100-1112

ABSTRACT

Colored semi-transparent Cu-Si oxide thin films have been prepared by reactive magnetron sputtering from a single cathode of copper-silicon composition. Thin films of different composition and optical response were obtained by changing process parameters like the relative amount of copper in the target and the O2/Ar mixture of the reactive plasma gas. The film characteristics were analyzed by several techniques. Their optical properties (refractive index, absorption coefficient, color) have been correlated with the process parameters used in the film preparation as well as with the film stoichiometry and chemistry.


Septiembre, 2011 | DOI: 10.1364/OME.1.001100

Boron Compounds as Stabilizers of a Complex Microstructure in a Co-B-based Catalyst for NaBH4 Hydrolysis


Arzac, G.M., Rojas, T.C., Fernández, A.
ChemCatChem, 3 (2011) 1305-1313

ABSTRACT

Co-B-based materials are widely used as catalysts for hydrogen generation through sodium borohydride self-decomposition. In the mid 1990s, the aqueous and organic chemistry involved in Co-B synthesis and handling was studied. Nevertheless, the exact microstructure of these catalysts has remained unsolved. Herein we present an exhaustive study which shows a new and complete microstructural view of a Co-B-based material together with the chemistry of the cobalt and boron involved. By using nanoscale-resolution microscopy and spectroscopy techniques, we have elucidated the role of boron compounds as stabilizers in a complex microstructure, which also explains its high catalytic performance and long-term stability. The catalyst is proposed to be made up of 1-3nm hcp Co0 nanoparticles embedded in amorphous CoxB (x=1, 2, 3), CoxOy, Co(BO2)2, and B2O3 phases alternatively or all together. All of these amorphous phases protect the nanocrystalline metallic core from growth and oxidation.


Agosto, 2011 | DOI: 10.1002/cctc.201100101

Aspects of heterogeneous enantioselective catalysis by metals


Kyriakou, G., Beaumont, S.K., Lambert, R.M.
Langmuir, 27 (2011) 9687-9695

ABSTRACT

Some aspects of metal-catalyzed heterogeneous enantioselective reactions are reviewed with specific reference to four different systems where the phenomena that control enantioselection appear to be very different. In the case of glucose electro-oxidation, it is clear that any intrinsic chirality present at the metal surface plays a vital role. With &#945;-keto hydrogenation, achiral surfaces modified by the adsorption of chiral agents become effective enantioselective catalysts and the formation of extended arrays of chiral species appears not to be of importance: instead a 1:1 docking interaction controlled by hydrogen bonding between the adsorbed chiral modifier and the prochiral reactant determines the outcome. Hydrogen bonding also plays a central role in &#946;-ketoester hydrogenation, but here fundamental studies indicate that the formation of ordered arrays involving the reactant and chiral ligand is of importance. Asymmetric C=C hydrogenation, though relatively little studied, has the potential for major impact in synthetic organic chemistry both on the laboratory scale and in the manufacture of fine chemicals and pharmaceuticals. The structural attributes that determine whether a given chiral ligand is effective have been identified; the ability to form strong covalent bonds with the metal surface while also resisting hydrogenation and displacement by the strongly adsorbing reactant under reaction conditions is an essential necessary condition. Beyond this, ligand rigidity in the vicinity of the chirality center coupled with resistance to SAM formation is a critically important factor whose absence results in racemic chemistry.


Agosto, 2011 | DOI: 10.1021/la200009w

Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films: Influence on the Electrical and Optical Properties


Manuel David Abad, Rosendo Sanjinés, Jose Luis Endrino, Raúl Gago, Joakim Andersson, Juan Carlos Sánchez-López
Plasma Processes and Polymers, 8 (2011) 579-588

ABSTRACT

The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB2 (60:40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiBxCy) or mixed binary (TiB2 and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K- and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiBxCy compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiBxCy phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.


Julio, 2011 | DOI: 10.1002/ppap.201000182

Bacterial adherence on UHMWPE with vitamin E: an in vitro study


E. Gómez-Barrena, J. Esteban, D. Molina-Manso, H. Adames, M.J. Martínez-Morlanes, A. Terriza, F. Yubero and J. A. Puértolas
Journal of Materials Science: Materials in Medicine, 22 (2011) 1701-1706

ABSTRACT

Orthopaedic materials may improve its capacity to resist bacterial adherence, and subsequent infection. Our aim was to test the bacterial adherence to alpha-tocopherol (frequently named vitamin E, VE) doped or blended UHMWPE with S. aureus and S. epidermidis, compared to virgin material. Collection strains and clinical strains isolated from patients with orthopaedic infections were used, with the biofilm-developing ability as a covariable. While collection strains showed significantly less adherence to VE-UHMWPE, some clinical strains failed to confirm this effect, leading to the conclusion that VE doped or blended UHMWPE affects the adherence of some S. epidermidis and S. aureus strains, independently of the concentration in use, but the results showed important intraspecies differences and cannot be generalized.


Julio, 2011 | DOI: 10.1007/s10856-011-4340-5

Mechanical, microstructural and oxidation properties of reactively sputtered thin Cr-N coatings on steel


Cecchini, R., Fabrizi, A., Cabibbo, M., Paternoster, C., Mavrin, B.N., Denisov, V.N., Novikova, N.N., Haïdopoulo, M.
Thin Solid Films, 519 (2011) 6515-6521

ABSTRACT

Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N2 flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr2N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N2. Also intrinsic coating hardness is influenced by both N2 flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.


Julio, 2011 | DOI: 10.1016/j.tsf.2011.04.115

Microstructure and chemical bonding of DLC films deposited on ACM rubber by PACVD


Martinez-Martinez, D., Schenkel, M., Pei, Y.T., Sánchez-López, J.C., De Hosson, J.T.H.M.
Surface and Coatings Technology, 205 (2011) S75-S78

ABSTRACT

The microstructure and chemical bonding of DLC films prepared by plasma assisted chemical vapor deposition on acrylic rubber (ACM) are studied in this paper. The temperature variation produced by the ion impingement during plasma cleaning and subsequent film deposition was used to modify the film microstructure by controlling the different degrees of strain applied to the substrate. The film microstructure is studied by top view and cross sectional SEM. The observed patch sizes are correlated with the variation of temperature that occurred during deposition. Finally, the chemical bonding of the samples is studied by Raman spectroscopy. All the samples show similar spectra regardless the bias voltage used.


Julio, 2011 | DOI: 10.1016/j.surfcoat.2011.02.067

Surface-functionalized fluorescent silica nanoparticles for the detection of ATP


Moro, AJ; Schmidt, J; Doussineau, T; Lapresta-Fernandez, A; Wegener, J; Mohr, GJ
Chemical Communications, 47 (2011) 6066-6068

ABSTRACT

The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(ii) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.


Junio, 2011 | DOI: 10.1039/C1CC10419E

Comparative investigation of Al- and Cr-doped TiSiCN coatings


D.V. Shtansky, K.A. Kuptsov, Ph.V. Kiryukhantsev-Korneev, A.N. Sheveiko, A. Fernandez and M.I. Petrzhik
Surface and Coatings Technology, 205 (2011) 4640-4648

ABSTRACT

The aim of this work was a comparative investigation of the structure and properties of Al- and Cr-doped TiSiCN coatings deposited by magnetron sputtering of composite TiAlSiCN and TiCrSiCN targets produced by self-propagating high-temperature synthesis method. Based on X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy data, the Al- and Cr-doped TiSiCN coatings possessed nanocomposite structures (Ti,Al)(C,N)/a-(Si,C) and (Ti,Cr)(C,N)/a-SiCxNy/a-C with cubic crystallites embedded in an amorphous matrix. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum at 1000, 1100, 1200, and 1300°C or in air at 1000°C for 1h. The results obtained show that the hardness of the Al-doped TiSiCN coatings increased from 41 to 46GPa, reaching maximum at 1000°C, and then slightly decreased to 38GPa at 1300°C. The Cr-doped TiSiCN coatings demonstrated high thermal stability up to 1100°C with hardness above 34GPa. Although both Al- and Cr-doped TiSiCN coatings possessed improved oxidation resistance up to 1000°C, the TiAlSiCN coatings were more oxidation resistant than their TiCrSiCN counterparts. The TiCrSiCN coatings showed better tribological characteristics both at 25 and 700°C and superior cutting performance compared with the TiAlSiCN coatings.


Junio, 2011 | DOI: 10.1016/j.surfcoat.2011.04.012

Surface-modified Pd and Au nanoparticles for anti-wear applications


J.C. Sánchez-López, M.D. Abad, L. Kolodziejczyk, E. Guerrero and A. Fernández
Tribology International, 44 (2011) 720-726

ABSTRACT

This work reports the employment of metallic nanoparticles (palladium and gold) with a mean particle size of 2.2 nm surface-protected with tetraalkylammonium and alkanethiolate chains, respectively, as lubricant additives. Dispersions of both types of nanoparticles (5 wt%) are prepared using tetrabutylammonium acetate (TBA) and paraffin as base oils, respectively. The tribological properties are then evaluated by a ball-on-disc tribometer at two different loads (7 and 15 N) with excellent results: friction (<0.1), wear rate (not, vert, similar10&#8722;10 mm3/Nm). The excellent anti-wear response is explained by the formation of a metal-containing transfer film and their action as counterface spacers avoiding direct contact.


Junio, 2011 | DOI: 10.1016/j.triboint.2009.12.013

Supported plasma-made 1D heterostructures: Perspectives and applications


Borras, A; Macias-Montero, M; Romero-Gomez, P; Gonzalez-Elipe, AR
Journal of Physics D: Applied Physics, 44 (2011) 174016

ABSTRACT

Plasma-related methods have been widely used in the fabrication of carbon nanotubes and nanofibres (NFs) and semiconducting inorganic nanowires (NWs). A natural progression of the research in the field of 1D nanostructures is the synthesis of multicomponent NWs and NFs. In this paper we review the state of the art of the fabrication by plasma methods of 1D heterostructures including applications and perspectives. Furthermore, recent developments on the use of metal seeds (Ag, Au, Pt) to obtain metal@oxide nanostructures are also extensively described. Results are shown for various metal substrates, either metal foils or supported nanoparticles/thin films of the metal where the effects of the size, surface coverage, percolation degree and thickness of the metal seeds have been systematically evaluated. The possibilities of the process are illustrated by the preparation of nanostructured films and supported NFs of different metal@oxides (Ag, Au and SiO2, TiO2, ZnO). Particularly, in the case of silver, the application of an oxygen plasma treatment prior to the deposition of the oxide was critical for efficiently controlling the growth of the 1D heterostructures. A phenomenological model is proposed to account for the thin-film nanostructuring and fibre formation by considering basic phenomena such as stress relaxation, inhomogeneities in the plasma sheath electrical field and the local disturbance of the oxide growth.


Mayo, 2011 | DOI: 10.1088/0022-3727/44/17/174016

Hydroxyapatite Synthesis on Mesoporous Silica: A High Resolution Electron Microscopy Study


D.R. Acosta, A. Díaz-Cuenca, A.
Acta Microscopica, 20 (2011) 29-35

ABSTRACT

En este trabajo se presentan resultados de la síntesis de hidroxiapatita  (HA)  en sílice mesoporosa SBA-15. Se ha hecho un estudio de la síntesis de ambos materiales y un seguimiento del efecto del doble tratamiento térmico posterior a la síntesis. Las muestras se sometieron a distintas temperaturas de tratamiento hidrotermal entre 353 y 393 K con incrementos de 10 K durante 24 horas. En cada caso y una vez filtrado y seco el material se volvió a tratar con una calcinación a 773 K durante 10 hs. Se presentan los resultados del estudio del material compuesto SBA-15-HA por microscopia electrónica de transmisión convencional y avanzada  ( STEM, Contraste Z, HREM) . El crecimiento de HA en los túneles de la matriz de sílice mesoporosa y el nivel de ocupación de los mismos aumenta con la temperatura del primer tratamiento hidrotermal y también del segundo tratamiento que favorece el sinterizado dentro de los túneles.


Mayo, 2011 | DOI:

Determination of Pore Size Distribution at the Cell-Hydrogel Interface


Leal-Egana, A., Dietrich-Braumann, U., Diaz-Cuenca, A., Nowicki, M., Bader, A.
Journal of Nanobiotechnology, 9 (2011) Page 24

ABSTRACT

Analyses of the pore size distribution in 3D matrices such as the cell-hydrogel interface are very useful when studying changes and modifications produced as a result of cellular growth and proliferation within the matrix, as pore size distribution plays an important role in the signaling and microenvironment stimuli imparted to the cells. However, the majority of the methods for the assessment of the porosity in biomaterials are not suitable to give quantitative information about the textural properties of these nano-interfaces.


Mayo, 2011 | DOI: 10.1186/1477-3155-9-24

Novel guests for porous columnar thin films: The switchable perchlorinated trityl radical derivatives


Oliveros, M; Gonzalez-Garcia, L; Mugnaini, V; Yubero, F; Roques, N; Veciana, J; Gonzalez-Elipe, AR; Rovira, C
Langmuir, 27 (2011) 5098-5106

ABSTRACT

TiO2 and SiO2 porous thin films consisting of tilted nanocolumns prepared by glancing angle evaporation (GLAD) have been infiltrated with guest derivatives belonging to the family of perchlorinated trityl radicals, novel guest molecules presenting an open-shell electronic configuration associated with paramagnetism, fluorescence, and electroactivity. The main driving forces for infiltration from aqueous solutions of the carboxylate-substituted radical derivatives are the electrostatic interactions between their negative charge and the net positive charges induced on the film pores. Positive charges on the internal surface of the films were induced by either adjusting the radical solution pH at values lower than the point of zero charge (PZC) of the oxide or passivating the nanocolumns oxide surface with a positively charged aminosilane. The infiltrated composite thin films are robust and easy to handle thanks to the physical protection exerted by the film columns. They also keep the multifunctionality of the used guests, as confirmed by electron paramagnetic resonance (EPR), UV-vis spectroscopy, and fluorescence spectroscopy. To prove the electroactivity of the infiltrated porous films, a porous TiO2 host layer was supported onto conductive indium tin oxide (ITO). By application of an appropriate redox potential, the guest radical molecules have been reversibly switched from their open-shell electronic configuration to their diamagnetic state and hence changed their optical properties. On the basis of these results, it is herein proposed that the appropriate surface functionalization of the pore internal surface of GLAD thin films can be used to prepare novel radical-oxide composite thin films usable for the development of robust switchable electrically driven photonic and magnetic devices.


Abril, 2011 | DOI: 10.1021/la200470f

Rhodamine 6G and 800 J-heteroaggregates with enhanced acceptor luminescence (HEAL) adsorbed in transparent SiO2 GLAD thin films


Sanchez-Valencia, JR; Aparicio, FJ; Espinos, JP; Gonzalez-Elipe, AR; Barranco, A
Physical Chemistry Chemical Physics, 13 (2011) 7071-7082

ABSTRACT

An enhanced fluorescent emission in the near infrared is observed when the Rhodamine 800 (Rh800) and 6G (Rh6G) dyes are coadsorbed in porous SiO 2 optical thin films prepared by glancing angle deposition (GLAD). This unusual behavior is not observed in solution and it has been ascribed to the formation of a new type of J-heteroaggregates with enhanced acceptor luminescence (HEAL). This article describes in detail and explains the main features of this new phenomenology previously referred in a short communication [J. R. Sánchez-Valencia, J. Toudert, L. González-García, A. R. González-Elipe and A. Barranco, Chem. Commun., 2010, 46, 4372-4374]. It is found that the efficiency and characteristics of the energy transfer process are dependent on the Rh6G/Rh800 concentration ratio which can be easily controlled by varying the pH of the solutions used for the infiltration of the molecules or by thermal treatments. A simple model has been proposed to account for the observed enhanced acceptor luminescence in which the heteroaggregates order themselves according to a "head to tail" configuration due to the geometrical constrains imposed by the SiO2 porous matrix thin film. The thermal stability of the dye molecules within the films and basic optical (absorption and fluorescence) principles of the HEAL process are also described.


Abril, 2011 | DOI: 10.1039/c0cp02421j

A comparative study of the role of additive in the MgH2 vs. the LiBH4&#8211;MgH2 hydrogen storage system


A. Fernández, E. Deprez, O. Friedrichs
International Journal of Hydrogen Energy, 36 (2011) 3932-3940

ABSTRACT

The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH2 single hydride and the MgH2 + 2LiBH4 reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB2 phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems.


Marzo, 2011 | DOI: 10.1016/j.ijhydene.2010.12.112

Nitridation of nanocrystalline TiO2 thin films by treatment with ammonia


Romero-Gomez, P; Rico, V; Espinos, JP; Gonzalez-Elipe, AR; Palgrave, RG; Egdell, RG
Thin Solid Films, 519 (2011) 3587-3595

ABSTRACT

Nanocrystalline anatase (TiO2) thin films prepared by a physical vapour deposition method were nitrided by annealing in flowing NH3 at temperatures ranging between 650 °C and 700 °C. It was established that there was a narrow window of temperatures which allowed both incorporation of interstitial nitrogen into the films with retention of the anatase phase without chemical reduction and preservation of the characteristic nanocrystalline morphology. These optimally modified films responded to visible light in photowetting tests and showed the ability to degrade an organic dye under visible light irradiation.


Marzo, 2011 | DOI: 10.1016/j.tsf.2011.01.267

Endurance of TiAlSiN coatings: Effect of Si and bias on wear and adhesion


Philippon, D; Godinho, V; Nagy, PM; Delplancke-Ogletree, MP; Fernandez, A
Wear, 270 (2011) 541-549

ABSTRACT

In this work, the endurance of TiAlSiN nanocomposite thin films subjected to tribological solicitation is studied. These coating were deposited on M2 steel substrate by magnetron sputtering. Dry sliding experiments were conducted at ambient temperature against WC-Co ball. Coefficients of friction, wear rates and endurances were correlated with the composition, microstructure, mechanical properties, residual stress and adhesion of the coatings. The hardness and elastic modulus were found dependent not only on the composition but also on the residual stress induced by the deposition process. Friction coefficient was found to be independent on Si content while the wear rate is strongly reduced for higher Si contents. The formation of a nanocomposite microstructure, the amount of amorphous Si-based phase and both, wear resistance and adhesion are shown as the critical factors to determine the endurance of the coating.


Marzo, 2011 | DOI: 10.1016/j.wear.2011.01.009

Selective Dichroic Patterning by Nanosecond Laser Treatment of Ag Nanostripes


Sanchez-Valencia, JR; Toudert, J; Borras, A; Barranco, A; Lahoz, R; de la Fuente, GF; Frutos, F; Gonzalez-Elipe, AR
Advanced Materials, 23 (2011) 848-853

ABSTRACT

A simple route for the fabrication of dichroic optical structures based on Ag nanoparticles deposited onto SiO2 nanocolumns is presented. The strict control of the optical response is achieved after infrared laser treatment of the supported nanoparticles with a commercial nanosecond pulsed laser. Preliminary examples of the utilization of the laser-treated AgNPs/SiO2 nanocolumn system for optical recoding and encryption are shown.


Febrero, 2011 | DOI: 10.1002/adma.201003933

Transparent Nanometric Organic Luminescent Films as UV-Active Components in Photonic Structures


Aparicio, FJ; Holgado, M; Borras, A; Blaszczyk-Lezak, I; Griol, A; Barrios, CA; Casquel, R; Sanza, FJ; Sohlstrom, H; Antelius, M; Gonzalez-Elipe, AR; Barranco, A
Advanced Materials, 23 (2011) 761-765

ABSTRACT

A new kind of visible-blind organic thin-film material, consisting of a polymeric matrix with a high concentration of embedded 3-hydroxyflavone (3HF) dye molecules, that absorbs UV light and emits green light is presented. The thin films can be grown on sensitive substrates, including flexible polymers and paper. Their suitability as photonic active components photonic devices is demonstrated.


Febrero, 2011 | DOI: 10.1002/adma.201003088

Influence of OH− concentration on the illitization of kaolinite at high pressure


M. Mantovani, A. Escudero, A.I. Becerro,
Applied Clay Science, 51 (2011) 220-225

ABSTRACT

The products of hydrothermal reactions of kaolinite at 300 °C and 1000 bars were studied in KOH solutions covering an OH concentration, [OH], of 1 M to 3.5 M. XRD patterns indicated a notable influence of the [OH] on the reaction. At [OH] ≥ 3 M, the only stable phase was muscovite/illite. The content of muscovite/illite was calculated from the analysis of the diagnostic 060 reflections of kaolinite and muscovite/illite. The results showed a linear dependence of kaolinite and muscovite/illite contents with [OH]. 27Al MAS NMR spectroscopy revealed the formation of small nuclei of K-F zeolite at high [OH]. Finally, modelling of the 29Si MAS NMR spectra indicated that the Si/Al ratio of the muscovite/illite formed was very close to that of muscovite, at least in the mineral formed at low [OH]. In good agreement with the XRD data, the quantification of the reaction products by 29Si MAS NMR indicated a linear decrease of the kaolinite content with increasing OH concentration.


Febrero, 2011 | DOI: 10.1016/j.clay.2010.11.021

Lateral and in-depth distribution of functional groups on diamond-like carbon after oxygen plasma treatments


Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Diamond and Related Materials, 20 (2011) 49-56

ABSTRACT

A diamond like carbon material has been exposed to a low pressure microwave and atmospheric pressure plasma of oxygen to enhance its hydrophilicity and surface energy. For comparison, data are also reported after activation with a beam of neutral atoms of oxygen. The surface incorporation of oxygenated functional groups and the determination of the in-depth distribution of this element have been analysed by means of the X ray photoemission spectroscopy (XPS). Atomic force microscopy (AFM) has been used to get information of the surface topography and, by recording friction maps of the surface, the lateral distribution of oxygenated functional groups formed after the different activation treatments. Differences in surface composition, topography and in-depth and lateral distribution of oxygen have been correlated with the intrinsic characteristics of the activation plasma processes.


Febrero, 2011 | DOI: 10.1016/j.diamond.2010.11.024

Nitrogen plasma functionalization of low density polyethylene


Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Surface and Coatings Technology, 205 (2011) 3356-3365

ABSTRACT

Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N2 and mixtures Ar+NH3 as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar+NH3 was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.


Febrero, 2011 | DOI: 10.1016/j.surfcoat.2010.11.038

Enhanced photoactivity in bilayer films with buried rutile-anatase heterojunctions


Romero-Gomez, P; Borras, A; Barranco, A; Espinos, JP; Gonzalez-Elipe, AR
ChemPhysChem, 12 (2011) 191-196

ABSTRACT

Herein, we study the photoactivity of anatase–rutile bilayer thin films consisting of an anatase overlayer of variable thickness from some tenths to some hundred nanometers deposited onto a rutile thin film. As references single anatase layers of equivalent thickness were deposited onto silicon. All the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The photoactivity of the samples was assessed by following the evolution with the UV illumination time of both the wetting angle on the thin film surface and the decoloration of a dye in a water solution. While a similar efficiency is found for the first type of experiments irrespective of the anatase thickness, in the second type a maximum in the photoactivity is found for a thickness of the anatase layer of about 130 nm. This enhanced photoactivity in bilayer systems with a buried anatase–rutile heterojunction is related to the formation of different Schottky potential barriers in the anatase layer, depending on its thickness and the substrate (i.e. rutile or SiO2) where it is deposited.


Enero, 2011 | DOI: 10.1002/cphc.201000734

Combined x-ray photoelectron spectroscopy and scanning electron microscopy studies of the LiBH4-MgH2 reactive hydride composite with and without a Ti-based additive


Deprez, E; Munoz-Marquez, MA; de Haro, MCJ; Palomares, FJ; Soria, F; Dornheim, M; Bormann, R; Fernandez, A
Journal of Applied Physics, 109 (2011) 014913 (10 pages)

ABSTRACT

A detailed electronic and microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite system with and without titanium isopropoxide as additive. Surface characterization by x-ray photoelectron spectroscopy combined to a morphological study by scanning electron microscopy as well as elemental map composition analysis by energy dispersive x-ray emission are presented in this paper for the first time for all sorption steps. Although sorption reactions are not complete at the surface due to the unavoidable superficial oxidation, it has been shown that the presence of the additive is favoring the heterogeneous nucleation of the MgB2 phase. Ti-based phases appear in all the samples for the three sorption steps well dispersed and uniformly distributed in the material. Li-based phases are highly dispersed at the surface while the Mg-based ones appear, either partially covered by the Li-based phases, or forming bigger grains. Ball milling is promoting mixing of phases and a good dispersion of the additive what favors grain refinement and heterogeneous reactions at the interfaces.


Enero, 2011 | DOI: 10.1063/1.3525803



2010


Tunable Nanostructure and Photoluminescence of Columnar ZnO Films Grown by Plasma Deposition


Romero-Gomez, P; Toudert, J; Sanchez-Valencia, JR; Borras, A; Barranco, A; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 114 (2010) 20932-20940

ABSTRACT

Nanoporous ZnO thin films presenting a tunable nanostructure and photoluminescence (PL) were grown by plasma enhanced vapor deposition on surface oxidized Si substrates. These films consist of c-axis oriented wurtzite ZnO nanocolumns whose topology, crystallinity, and PL can be tuned through the substrate temperature (varied in the 300-573 K range) and the nature of the plasma assistance (pure O-2, O-2/Ar, O-2/H-2, or O-2/N-2 mixture). In particular, these processing parameters influence the intensity of the UV and visible PL bands of the films, related to excitonic and defective radiative transitions, respectively. Increasing the substrate temperature enhances the UV PL and rubs out the visible PL due to the increase of grain size and the removal of interstitial defects. Additional tuning of the intensity ratio between the UV and visible bands can be done by controlling the film thickness. A decrease of the UV PL is observed when the films go thicker, an effect that is likely to be linked to the microstructure of the films rather than to their crystallinity that is improved upon increasing of the film thickness, as seen from PL spectroscopy and XRD measurements. Indeed, a gradient of stress, decreasing from the substrate to the surface, is evidenced and related to a concentration gradient of interstitial defects. The drawbacks of the thickness effect, which prohibits growing thick films with a high optical quality, can be bypassed by growing the films in a O-2/H-2 plasma.


Diciembre, 2010 | DOI: 10.1021/jp103902u

Band Gap Narrowing versus Formation of Electronic States in the Gap in N-TiO2 Thin Films


Romero-Gomez, P; Hamad, S; Gonzalez, JC; Barranco, A; Espinos, JP; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 114 (2010) 22546-22557

ABSTRACT

N-containing TiO2 thin films with different amounts of nitrogen have been prepared by plasma enhanced chemical vapor deposition (PECVD) by using different titanium precursors without (titanium isopropoxide, TTIP) and with (tetrakis diethylamino titanium, TDEAT and tetrakis dimethylamino titanium, TDMAT) nitrogen in their structures and different N-2/O-2 ratios as plasma gas. For low/high content of nitrogen, Ti-NO- and/or Ti-N-like species have been detected in the films by X-ray photoelectron spectroscopy (XPS). Their optical behavior is characterized by a red shift of their absorption edge when Ti-N species are a majority, and by an unmodified edge with localized absorption states in the gap when only Ti-NO-like species are present in the film. The experimental results have been interpreted by calculating the density of states of model systems consisting of a 2 x 2 x 3 repetition of the anatase unit cell. This basic structure incorporates nitrogen defects in either substitutional or interstitial lattice positions that are considered equivalent to the Ti-N- and Ti-NO-like species detected by XPS. To simulate the effect of, respectively, a low or a high concentration of nitrogen, calculations have been carried out by placing two nitrogen defects either in separated or in nearby positions of the anatase structure. The computational analysis reveals that the defects have different stabilization energies and confirm that an edge shift of the valence band is induced by the substitutional nitrogen centers, as observed when a high concentration of Ti-N species becomes incorporated into the films. In agreement with the experimental results, when only Ti-NO-like species are detected by XPS, no band gap narrowing is obtained by the calculations that predict the appearance of localized electronic states in the gap. The fact that only these latter films present water wetting angle photoactivity when irradiated with visible light supports that the presence of Ti-NO-like species is a required condition for visible light photoactivity.


Diciembre, 2010 | DOI: 10.1021/jp104634j

Effect of process parameters on mechanical and tribological performance of pulsed-DC sputtered TiC/a-C:H nanocomposite films


Shaha, KP; Pei, YT; Martinez-Martinez, D; Sanchez-Lopez, JC; De Hosson, JTM
Surface and Coatings Technology, 205 (2010) 2633-2642

ABSTRACT

Mechanical, structural, chemical bonding (sp(3)/sp(2)). and tribological properties of films deposited by pulsed-DC sputtering of Ti targets in Ar/C2H2 plasma were studied as a function of the substrate bias voltage, Ti-target current, C2H2 flow rate and pulse frequency by nanoindentation, Raman spectroscopy and ball-on-disc tribometry. The new findings in this study comprise: dense, column-free, smooth, and ultra-low friction TiC/a-C:H films are obtained at a lower substrate bias voltage by pulsed-DC sputtering at 200 and 350 kHz frequency. The change in chemical and phase composition influences the tribological performance where the TiC/a-C:H films perform better than the pure a-C:H films. In the case of TiC/a-C:H nanocomposite films, a higher sp(2) content and the presence of TiC nanocrystallites at the sliding surface promote formation of a transfer layer and yield lower friction. In the case of a-C:H films, a higher sp(3) content and higher stress promote formation of hard wear debris during sliding, which cause abrasive wear of the ball counterpart and yield higher friction.


Diciembre, 2010 | DOI: 10.1016/j.surfcoat.2010.10.020

Illization of kaolinite: The effect of pressure on the reaction rate


Mantovani, M; Becerro, AI
Clays and Clay Minerals, 58 (2010) 766-771

ABSTRACT

Studies of the paragenesis of authigenic illite in arkosic sandstonesof various regions and ages have revealed that the illitizationof kaolinite is an important reaction accounting for the formationof authigenic illite in sandstones during burial diagenesis.The illitization of kaolinite takes place at an intermediateburial depth of 3–4 km, where pressure can reach valuesof 100 MPa ({approx}1000 bars). The purpose of the present study wasto analyze the effect of pressure on the rate of kaolinite illitizationin alkaline conditions. Hydrothermal reactions were conductedon KGa-1b kaolinite in KOH solution at 300°C and under pressuresof 500, 1000, and 3000 bars for 1 to 24 h. The visual examinationof the X-ray diffraction (XRD) patterns indicated a notableinfluence of pressure on the reaction rate. Molar percentagesof muscovite/illite formed at each time interval were calculatedfrom the analysis of two diagnostic XRD peaks, representingthe 060 reflections of kaolinite and muscovite/illite. The datawere modeled to obtain the initial rate of conversion at eachpressure. The results indicated that the initial rate of kaoliniteto muscovite/illite conversion is one order of magnitude greaterat 3000 bars than at 500 or 1000 bars. Comparison of these datawith those in the literature show a faster conversion rate (severalorders of magnitude) in an initially high-alkaline solutionthan in a near-neutral solution.


Diciembre, 2010 | DOI: 10.1346/CCMN.2010.0580604

Improved Non-Covalent Biofunctionalization of Multi-Walled Carbon Nanotubes Using Carbohydrate Amphiphiles with a Butterfly-Like Polyaromatic Tail


Assali, M; Leal, MP; Fernandez, I; Romero-Gomez, P; Baati, R; Khiar, N
Nano Research, 3 (2010) 764-778

ABSTRACT

We have developed an efficient strategy for the non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) which allows a biomimetic presentation of carbohydrates on their surface by pi-pi stacking interactions. The strategy is based on the use of sugar-based amphiphiles functionalized with tetrabenzo[a,c,g,i] fluorene (Tbf), a polyaromatic compound with a topology that resembles a butterfly with open wings. The new carbohydrate-tethered Tbf amphiphiles have been synthesized in a straightforward manner using click chemistry. The reported method has been developed in order to improve the rather low ability of pyrene-based systems to exfoliate MWCNTs in water. By means of thermogravimetric analysis (TGA), ultraviolet (UV), infrared (IR), and fluorescence spectroscopies the interaction between MWCNTs and the Tbf group has been found to be stronger than those involving pyrene-based amphiphilic carbohydrates. The resulting aggregates with a multivalent sugar exposition on their surface are able to engage in specific ligand-lectin interactions similar to glycoconjugates on a cell membrane.


Noviembre, 2010 | DOI: 10.1007/s12274-010-0044-2

Effect of pressure on kaolinite illitization


Mantovani, M; Escudero, A; Becerro, AI
Applied Clay Science, 50 (2010) 342-347

ABSTRACT

The illitization of kaolinite at increasing pressures was followed by hydrothermal experiments of kaolinite in KOH solution at 300 degrees C for 12 h and pressures between 500 and 3000 bar XRD indicated a direct transformation of kaolinite into muscovite/illite with increasing pressure However the (27)AI MAS NMR spectra showed in addition to the muscovite/illite resonances the presence of a signal at 61 ppm that should correspond to a secondary phase not detected by XRD A second series of experiments at 300 degrees C and 1000 bar for 1 3 and 6 h was carried out to show direct evidence of such phase The XRD patterns of the products clearly showed the crystallization of K-F zeolite while the (27)AI MAS NMR spectra of these samples displayed a signal at 61 ppm that must correspond therefore to Al in the K-F zeolite structure In conclusion kaolinite transformed into muscovite/illite when submitted to hydrothermal reaction in KOH solution with increasing pressure with the formation of a secondary metastable phase called K-F zeolite whose coherent diffraction domains were too small as to be detected by XRD.Effect of pressure on kaolinite illitization


Noviembre, 2010 | DOI: 10.1016/j.clay.2010.08.024

Wetting Properties of Polycrystalline TiO2 Surfaces: A Scaling Approach to the Roughness Factors


Borras, A; Gonzalez-Elipe, AR
Langmuir, 26 (2010) 15875-15882

ABSTRACT

This work presents a thorough study on the wettability of polycrystalline anatase TiO2 thin films prepared at 250 degrees C in a microwave plasma enhanced chemical vapor deposition (MW-PECVD) reactor with Ar/O-2 plasmas. Anatase polycrystalline thin films with different microstructures, textures, and surface roughness were obtained as a function of their thickness. The water contact angle of the samples was analyzed within the assumptions of the Wenzel, Cassie, and Miwa models to ascertain the effect of roughness and other surface heterogeneities on their characteristic parameters. The roughness factors defined in the different models were calculated from the atomic force microscopy (AFM) images of the films for two different observation scales within the premises of the dynamic scaling theories. The obtained results indicate that the wetting angle of an equivalent flat anatase surface with a value of 82 degrees can only be properly estimated for observation scales of 5 x 5 mu m(2) and using the Miwa model. The analysis of the UV induced hydrophilization of the surface state of the anatase films and the posterior recovery of the partially hydrophobic character of these surfaces in the absence of UV photons suggest a clear dependence of the light induced wettability on their texture and size of crystalline domains.


Octubre, 2010 | DOI: 10.1021/la101975e

Tilt angle control of nanocolumns grown by glancing angle sputtering at variable argon pressures


Garcia-Martin, JM; Alvarez, R; Romero-Gomez, P; Cebollada, A; Palmero, A
Applied Physics Letters, 97 (2010) - 173103

ABSTRACT

We show that the tilt angle of nanostructures obtained by glancing angle sputtering is finely tuned by selecting the adequate argon pressure. At low pressures, a ballistic deposition regime dominates, yielding high directional atoms that form tilted nanocolumns. High pressures lead to a diffusive regime which gives rise to vertical columnar growth. Monte Carlo simulations reproduce the experimental results indicating that the loss of directionality of the sputtered particles in the gas phase, together with the self-shadowing mechanism at the surface, are the main processes responsible for the development of the columns.


Octubre, 2010 | DOI: 10.1063/1.3506502

Microstructural study of the LiBH4-MgH2 reactive hydride composite with and without Ti-isopropoxide additive


Deprez, E; Justo, A; Rojas, TC; Lopez-Cartes, C; Minella, CB; Bosenberg, U; Dornheim, M; Borrnann, R; Fernandez, A
Acta Materialia, 58 (2010) 5683-5694

ABSTRACT

An exhaustive microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite (RHC) system with and without titanium isopropoxide additive. X-ray diffraction with Rietveld analysis, transmission electron microscopy coupled to energy dispersive X-ray analysis, selected-area electron diffraction and electron energy loss spectroscopy are presented in this paper for the first time for this system for all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology; these results contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions. Considerations on the stability of phases under electron beam irradiation have also been reported.


Octubre, 2010 | DOI: 10.1016/j.actamat.2010.06.043

A transparent TMPyP/TiO2 composite thin film as an HCl sensitive optochemical gas sensor


Cano, M; Castillero, P; Roales, J; Pedrosa, JM; Brittle, S; Richardson, T; Gonzalez-Elipe, AR; Barranco, A
Sensors and Actuators B-Chemical, 150 (2010) 764-769

ABSTRACT

Tetracationic porphyrin (TMPyP) molecules were incorporated Into an optically transparent TiO2 thin film prepared by Glancing Angle Physical Vapour Deposition (GAPVD) by simple infiltration (at pH 6 4) The preparation of optically transparent TMPyP/TiO2 composite thin films provides a method for the integration of the porphyrin molecules Into photonic devices for direct monitoring of gases Previously UV-visible and fluorescence spectral techniques have been used to study the reversible protonation of TMPyP in aqueous solution The optical spectrum of TMPyP shows an intense Soret band at 423 nm with a 22 nm red shift upon protonation by HCl The experimental conditions for monitoring the concentration of HCl gas by absorption spectroscopy have been optimized The maximum absorbance change was observed at the Sorer band wavelength A selected temperature of 80 C and a 300 s recovery period were found to be the optimum operating parameters (response time t(50) = 16 8  7 s) The composite with smaller surface concentration of TMPyP (Gamma = 03 x 10(-9) mol cm(-2)) presented the best detection limit (0 1 ppm) The response of the composite sensor was highly stable for several months.


Octubre, 2010 | DOI: 10.1016/j.snb.2010.07.059

Si-doped multifunctional bioactive nanostructured films


Shtansky, DV; Gloushankova, NA; Sheveiko, AN; Kiryukhantsev-Korneev, PV; Bashkova, IA; Mavrin, BN; Ignatov, SG; Filippovich, SY; Rojas, C
Surface and Coatings Technology, 205 (2010) 728-739

ABSTRACT

Si-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering of composite TiC0.5 + CaO + Si (A) and TiC0.5 + CaO + Si3N4 (B) targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, scanning and transmission electron microscopy, electron energy loss spectroscopy, glow discharge optical emission spectroscopy. Raman, and IR spectroscopy. The Ti-Si-Ca-P-C-O-(N) films consisted of TiC(N) as a main phase with a minor amount of TiOx, SiNx, SiOx, SiC, and CaO phases probably mainly in amorphous state at the grain boundaries and COO- groups on the film surface. The excess of carbon atoms in the Ti-Si-Ca-P-C-O-N film (target A) precipitated in a DLC form. The films showed hardness in the range of 26-31 GPa, reduced Young's modulus of 200-270 GPa, and high percentage of elastic recovery of 60-71%. The best Ti-Si-Ca-C-O-N films exhibited low friction coefficient both in physiological solution and Dulbecko modified Eagle medium with fetal calf serum, hydrophilic properties, improved electrochemical characteristics, and excellent impact resistance. Nevertheless, the wear resistance of the Ti-Si-Ca-C-O-N films against Al2O3 ball was lower compared with the best Si-free MuBiNaFs. In vitro studies showed that the Si-doped Ti-Ca-C-O-N films possess improved osteoconductive characteristics during early stage of cell/material interaction. The film surface was highly adhesive for IAR-2 epithelial and MC3T3-E1 osteoblastic cells. The films revealed a high level of biocompatibility and biostability in experiments in vivo. The Ti-Si-Ca-C-O-N film (target A) did not show any bactericidal activity during cultivation of bacterial strains both on solid and in liquid Luria Bertani mediums. The film did not reveal any bactericidal and toxic activity against macrophages and therefore did not change bacterial status and defence system of macro-organisms.


Octubre, 2010 | DOI: 10.1016/j.surfcoat.2010.07.063

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate


Hartmanova, M; Jergel, M; Holgado, JP; Espinos, JP
Vacuum, 85 (2010) 535-540

ABSTRACT

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500 degrees and 700 degrees C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 degrees C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 degrees C whereas no texture was found for 700 degrees C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.


Octubre, 2010 | DOI: 10.1016/j.vacuum.2010.09.003

Surface nanostructuring of TiO2 thin films by high energy ion irradiation


Romero-Gomez, P; Palmero, A; Ben, T; Lozano, JG; Molina, SI; Gonzalez-Elipe, AR
Physical Review B, 82 (2010) - 115420 (8 pages)

ABSTRACT

The effects of a high ion dose irradiation on TiO2 thin films under different conditions of temperature and ion nature are discussed. We have shown that anatase TiO2 thin films irradiated with N+ ions at room temperature develop a typical microstructure with mounds and voids open to the surface whereas irradiations at 700 K generate a surface pattern of well-ordered nanorods aligned with the ion beam. The formation of these patterns is caused by the simultaneous effect of ion irradiation near the film surface and a film temperature favoring the structural mobilization of the defective network of the material. To explain these phenomena, a qualitative model has been proposed and further tested by irradiating the TiO2 thin films with F+ and S+ ions under different conditions. The obtained results demonstrate that ion irradiation techniques enable the formation of tilted nanorod surface patterns with lengths of about 100 nm on anatase TiO2 thin films.


Septiembre, 2010 | DOI: 10.1103/PhysRevB.82.115420

Tunable In-Plane Optical Anisotropy of Ag Nanoparticles Deposited by DC Sputtering onto SiO2 Nanocolumnar Films


Sanchez-Valencia, JR; Toudert, J; Borras, A; Lopez-Santos, C; Barranco, A; Feliu, IO; Gonzalez-Elipe, AR
Plasmonics, 5 (2010) 241-250

ABSTRACT

This work reports an easy-to-handle method for growing two-dimensional assemblies of Ag nanostructures presenting a tunable in-plane optical anisotropy. Ag is deposited by DC sputtering in an Ar plasma at room temperature onto bundled nanocolumnar SiO2 thin films grown by glancing angle physical vapor deposition. In contrast with previously reported processes involving the grazing angle deposition of the metal, DC sputtering is performed at normal incidence. By varying the deposition angle of SiO2 and the Ar pressure, it was possible to tune the deposited amount of Ag and thus the topology of the Ag deposit from isolated spherical Ag nanoparticles with isotropic optical properties to strongly dichroic Ag nanostripes oriented along the bundling direction of the SiO2 nanocolumns. Based on simple calculations taking into account the shadowing effects during metal deposition, it is proposed that the width and shape of the tip of the bundled SiO2 nanocolumns influence significantly the metal local atom flux arriving to them and thus the final structure of the deposit.


Septiembre, 2010 | DOI: 10.1007/s11468-010-9139-6

On the microstructure of thin films grown by an isotropically directed deposition flux


Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Palmero, A; Gonzalez-Elipe, AR
Journal of Applied Physics, 108 (2010) 64316

ABSTRACT

The influence of isotropically directed deposition flux on the formation of the thin film microstructure at low temperatures is studied. For this purpose we have deposited TiO2 thin films by two different deposition techniques: reactive magnetron sputtering, in two different experimental configurations, and plasma enhanced chemical vapor deposition. The obtained results indicate that films grown under conditions where deposition particles do not possess a clear directionality, and in the absence of a relevant plasma/film interaction, present similar refractive indices no matter the deposition technique employed. The film morphology is also similar and consists of a granular surface topography and a columnarlike structure in the bulk whose diameter increases almost linearly with the film thickness. The deposition has been simulated by means of a Monte Carlo model, taking into account the main processes during growth. The agreement between simulations and experimental results indicates that the obtained microstructures are a consequence of the incorporation of low-energy, isotropically directed, deposition particles.


Septiembre, 2010 | DOI: 10.1063/1.3483242

Characterization of Ti1-xAlxN coatings with selective IR reflectivity


Godinho, V; Philippon, D; Rojas, TC; Novikova, NN; Yakovlev, VA; Vinogradov, EA; Fernandez, A
Solar Energy, 84 (2010) 1397-1401

ABSTRACT

Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The obtained different stoichiometries give rise to different optical properties as the films change from metallic to dielectric. In this work the IR reflectivity of these coatings is investigated taking into account different application fields for IR selective Ti1-xAlxN thin films. Low Al content coatings present high reflectivity, high absorptance and low thermal emittance. High Al compositions give raise to coatings with high absorptance and high thermal emittance. The composition of the coatings was evaluated combining electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy. Scanning electron microscopy (SEM) revealed a columnar structure. Reflectance spectra for the visible and infrared spectral ranges were used to obtain the solar absorptance and thermal emittance values, used to calculate the equilibrium temperature of the coatings. The thermal stability in air from 300 to 600 degrees C was also evaluated.


Agosto, 2010 | DOI: 10.1016/j.solener.2010.04.021

Tailored synthesis of nanostructured WC/a-C coatings by dual magnetron sputtering


Abad, MD; Munoz-Marquez, MA; El Mrabet, S; Justo, A; Sanchez-Lopez, JC
Surface and Coatings Technology, 204 (2010) 3490-3500

ABSTRACT

Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation. the WC nanocrystalline phases evolve from gamma-W2C to beta-WC1-x. Further C enrichment leads to a nanocomposite structure of small WC1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; mu=0.6-0.8) to moderate-hard/low friction (16-20 GPa; mu similar to 0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC1-x/a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.


Agosto, 2010 | DOI: 10.1016/j.surfcoat.2010.04.019

TiO2-SiO2 one-dimensional photonic crystals of controlled porosity by glancing angle physical vapour deposition


Gonzalez-Garcia, L; Lozano, G; Barranco, A; Miguez, H; Gonzalez-Elipe, AR
Journal of Materials Chemistry, 20 (2010) 6408-6412

ABSTRACT

Herein we present a synthetic route to attain porous one-dimensional photonic crystals of high optical quality. The method employed, based on the alternate deposition of TiO2 and SiO2 porous layers by glancing angle physical vapour deposition, yields a highly accessible interconnected pore network throughout the entire multilayer structure. Furthermore, it allows a strict control over the average size and density of the interstitial sites, which results in the precise tuning of the refractive index of the individual layers and thus of the optical response of the ensemble. The controlled environmental response of the multilayer is confirmed by the optical monitoring of the infiltration of liquids of different refractive index.


Agosto, 2010 | DOI: 10.1039/C0JM00680G

Effect of surface roughness and sterilization on bacterial adherence to ultra-high molecular weight polyethylene


Kinnari, TJ; Esteban, J; Zamora, N; Fernandez, R; Lopez-Santos, C; Yubero, F; Mariscal, D; Puertolas, JA; Gomez-Barrena, E
Clinical Microbiology and Infection, 16 (2010) 1036-1041

ABSTRACT

Sterilization with ethylene oxide (EO) and gas plasma (GP) are well-known methods applied to ultra-high molecular weight polyethylene (UHMWPE) surfaces in the belief that they prevent major material changes caused by gamma irradiation. However, the influence of these surface sterilization methods on bacterial adherence to UHMWPE is unknown. UHMWPE samples with various degrees of roughness (0.3, 0.8 and 2.0 mu m) were sterilized with either GP or EO. The variations in hydrophobicity, surface free energy and surface functional groups were investigated before and after sterilization. Sterilized samples were incubated with either Staphylococcus aureus or Staphylococcus epidermidis in order to study bacterial adherence to these materials. Fewer bacteria adhered to UHMWPE after sterilization with EO than after sterilization with GP, especially to the smoothest surfaces. No changes in chemical composition of the UHMWPE surface due to sterilization were observed using X-ray photoemission spectroscopy analysis. The decreased bacterial adherence to UHMWPE found at the smoothest surfaces after sterilization with EO was not directly related to changes in chemical composition. Increased bacterial adherence to rougher surfaces was associated with increased polar surface energy of EO-sterilized surfaces.


Julio, 2010 | DOI: 10.1111/j.1469-0691.2009.02995.x/full

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small-Angle X-ray Scattering


Gonzalez-Garcia, L; Barranco, A; Paez, AM; Gonzalez-Elipe, AR; Garcia-Gutierrez, MC; Hernandez, JJ; Rueda, DR; Ezquerra, TA; Babonneaum, D
Chemphyschem, 11 (2010) 2205-2208

ABSTRACT

For the first time, grazing incidence small-angle X-ray scattering (GISAXS) analysis is used to characterize the Morphology of TiO2 thin films grown by glancing angle physical vapor deposition (GLAD). According to cross-section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO2 columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the titled of the TiO2 columns. The patterns also show the existence of two populations of columns in these GLAD TiO2 films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.


Julio, 2010 | DOI: 10.1002/cphc.201000136

Influence of carbon chemical bonding on the tribological behavior of sputtered nanocomposite TiBC/a-C coatings


Abad, MD; Sanchez-Lopez, JC; Brizuela, M; Garcia-Luis, A; Shtansky, DV
Thin Solid Films, 518 (2010) 5546-5552

ABSTRACT

The tribological performance of nanocomposite coatings containing Ti-B-C phases and amorphous carbon (a-C) are studied. The coatings are deposited by a sputtering process from a sintered TiB2:TiC target and graphite, using pulsed direct current and radio frequency sources. By varying the sputtering power ratio, the amorphous carbon content of the coatings can be tuned, as observed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The crystalline component consists of very disordered crystals with a mixture of TiB2/TiC or TiBxCy phases. A slight increase in crystalline order is detected with the incorporation of carbon in the coatings that is attributed to the formation of a ternary TiBxCy phase. An estimation of the carbon present in the form of carbide (TiBxCy or TiC) and amorphous (a-C) is performed using fitting analysis of the C 1s XPS peak. The film hardness (22 to 31 GPa) correlates with the fraction of the TiBxCy phase that exists in the coatings. The tribological properties were measured by a pin-on-disk tribometer in ambient conditions, using 6 mm tungsten carbide balls at 1 N. The friction coefficients and the wear rates show similar behavior, exhibiting an optimum when the fraction of C atoms in the amorphous phase is near 50%. This composition enables significant improvement of the friction coefficients and wear rates (mu similar to 0.1; k < 1 x 10(-6) mm(3)/Nm), while maintaining a good value of hardness (24.6 GPa). Establishing the correlation between the lubricant properties and the fraction of a-C is very useful for purposes of tailoring the protective character of these nanocomposite coatings to engineering applications.


Julio, 2010 | DOI: 10.1016/j.tsf.2010.04.038

Preparation and structural properties of YBCO films grown on GaN/c-sapphire hexagonal substrate


Chromik, S; Gierlowski, P; Spankova, M; Dobrocka, E; Vavra, I; Strbik, V; Lalinsky, T; Sojkova, M; Liday, J; Vogrincic, P; Espinos, JP
Applied Surface Science, 256 (2010) 5618-5622

ABSTRACT

Epitaxial YBCO thin films have been grown on hexagonal GaN/c-sapphire substrates using DC magnetron sputtering and pulsed laser deposition. An MgO buffer layer has been inserted between the substrate and the YBCO film as a diffusion barrier. X-ray diffraction analysis indicates a c-axis oriented growth of the YBCO films. &#934;-scan shows surprisingly twelve maxima. Transmission electron microscopy analyses confirm an epitaxial growth of the YBCO blocks with a superposition of three a&#8211;b YBCO planes rotated by 120° to each other. Auger electron spectroscopy and X-ray photoelectron spectroscopy reveal no surface contamination with Ga even if a maximum substrate temperature of 700 °C is applied.


Julio, 2010 | DOI: 10.1016/j.apsusc.2010.03.035

Improved wear performance of ultra high molecular weight polyethylene coated with hydrogenated diamond like carbon


Puertolas, JA; Martinez-Nogues, V; Martinez-Morlanes, MJ; Mariscal, MD; Medel, FJ; Lopez-Santos, C; Yubero, F
WEAR, 269 (2010) 458-465

ABSTRACT

Hydrogenated diamond like carbon (DLCH) thin films were deposited on medical grade ultra high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition. The DLCH coating thicknesses ranged from 250 to 700 nm The substrates were disks made of UHMWPEs typically used for soft components in artificial Joints, namely virgin GUR 1050 and highly crosslinked (gamma irradiated in air to 100 kGy) UHMWPEs Mechanical and tribological properties under bovine serum lubrication at body temperature were assessed on coated and uncoated polyethylenes by means of nano-hardness and ball-on-disk tests, respectively Morphological features of the worn surfaces were obtained by confocal microscopy and scanning electron microscopy This study confirms an increase in surface hardness and good wear resistance for coated materials after 24 h of sliding test compared to uncoated polyethylene. These results point out that to coat UHMWPE with DLCH films could be a potential method to reduce backside wear in total hip and knee arthroplasties.


Julio, 2010 | DOI: 10.1016/j.wear.2010.04.033

Study of the morphology of NiO nanostructures grown on highly ordered pyrolytic graphite, by the Tougaard method and atomic force microscopy: a comparative study


Preda, I; Soriano, L; Alvarez, L; Mendez, J; Yubero, F; Gutierrez, A; Sanz, JM
Surface and Interface Analysis, 42 (2010) 869-873

ABSTRACT

We studied the morphology of the deposits of NiO grown on highly ordered pyrolytic graphite (HOPG), by means of inelastic peak shape analysis and atomic force microscopy. The results obtained by both techniques show an excellent agreement. The results indicate that NiO grows on HOPG by following the Stransky-Krastanov type of growth.


Junio, 2010 | DOI: 10.1002/sia.3222

Permanent magnetism in phosphine- and chlorine-capped gold: from clusters to nanoparticles


Munoz-Marquez, MA; Guerrero, E; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Journal of Nanoparticle Research, 12 (2010) 1307-1318

ABSTRACT

Magnetometry results have shown that gold NPs (similar to 2 nm in size) protected with phosphine and chlorine ligands exhibit permanent magnetism. When the NPs size decreases down to the subnanometric size range, e.g. undecagold atom clusters, the permanent magnetism disappears. The near edge structure of the X-ray absorption spectroscopy data points out that charge transfer between gold and the capping system occurs in both cases. These results strongly suggest that nearly metallic Au bonds are also required for the induction of a magnetic response. Electron paramagnetic resonance observations indicate that the contribution to magnetism from eventual iron impurities can be disregarded.


Mayo, 2010 | DOI: 10.1007/s11051-010-9862-0

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties


Godinho, V; de Haro, MCJ; Garcia-Lopez, J; Goossens, V; Terryn, H; Delplancke-Ogletree, MP; Fernandez, A
Applied Surface Science, 256 (2010) 4548-4553

ABSTRACT

In this work amorphous silicon oxynitride films with similar composition (ca. Si0.40N0.45O0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N-2-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus. The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N-2 gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.


Mayo, 2010 | DOI: 10.1016/j.apsusc.2010.02.045

Excitation transfer mechanism along the visible to the Near-IR in rhodamine J-heteroaggregates


Sanchez-Valencia, JR; Toudert, J; Gonzalez-Garcia, L; Gonzalez-Elipe, AR; Barranco, A
Chemical Communications, 46 (2010) 4372-4374

ABSTRACT

An enhanced fluorescent emission of the dye Rhodamine 800 in the Near-IR is observed in the presence of other xanthene dye molecules (RhX) when they are hosted in different matrices due to the formation of a new type of fluorescent J-heteroaggregates.

This enhanced emission of the acceptor occurs despite the low spectral overlapping and the low quantum yield of Rh800.


Mayo, 2010 | DOI: 10.1039/c0cc00087f

One-Step Dry Method for the Synthesis of Supported Single-Crystalline Organic Nanowires Formed by pi-Conjugated Molecules


Borras, A; Groning, O; Aguirre, M; Gramm, F; Groning, P
Langmuir, 26 (2010) 5763-5771

ABSTRACT

We present for the first time a general vacuum process for the growth of supported organic nanowires formed by pi-conjugated molecules, including metalloporphyrins, metallophthalocyanines, and perylenes. This methodology consists on a one-step physical vapor deposition of the pi-conjugated molecules. The synthesis is carried out at controlled temperature on substrates with tailor morphology which allows the growth or organic nanowires in the form of squared nanofibers and nanobelts. The study of the nanowires by electron diffraction and HRTEM combining with the results of a theoretical analysis of the possible arrangement of the pi-conjugated molecules along the nanowires reveals that the nanowires show a columnar structure along the fiber axis consisting of pi-stacked molecules having a herringbone-like arrangement. The formation of these nanowires on different substrates demonstrates that the growth mechanism is independent of the substrate chemical composition. An in-depth phenomenological study of the Formation of the nanowires drives us to propose a growth mechanism based on a crystallization process. Furthermore, the growth method allows the fabrication of two particular ID heterostructures: binary and open core@shell organic nanofibers.


Abril, 2010 | DOI: 10.1021/la1003758

Non-destructive depth compositional profiles by XPS peak-shape analysis


Lopez-Santos, MC; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR
Analytical and Bioanalytical Chemistry, 396 (2010) 2757-2768

ABSTRACT

The measured peak shape and intensity of the photoemitted signal in X-ray photoelectron spectroscopy (XPS) experiments (elastic and inelastic parts included) are strongly correlated, through electron-transport theory, with the depth distribution of photoelectron emitters within the analyzed surface. This is the basis of so-called XPS peak-shape analysis (also known as the Tougaard method) for non-destructive determination of compositional in-depth (up to 6-8 nm) profiles. This review describes the theoretical basis and reliability of this procedure for quantifying amounts and distributions of material within a surface. The possibilities of this kind of analysis are illustrated with several case examples related to the study of the initial steps of thin-film growth and the modifications induced in polymer surfaces after plasma treatments.


Abril, 2010 | DOI: 10.1007/s00216-009-3312-9

Surface Functionalization, Oxygen Depth Profiles, and Wetting Behavior of PET Treated with Different Nitrogen Plasmas


Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 2 (2010) 980-990

ABSTRACT

Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N-2 and mixtures Ar + NH3 as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard's method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH3 is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization by reaction with chlorobenzaldehyde. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated PET.


Abril, 2010 | DOI: 10.1021/am100052w

Active and Optically Transparent Tetracationic Porphyrin/TiO2 Composite Thin Films


Castillero, P; Sanchez-Valencia, JR; Cano, M; Pedrosa, JM; Roales, J; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 2 (2010) 712-721

ABSTRACT

Fluorescent tetracationic porphyrin (TMPyP) molecules have been incorporated into optically transparent TiO2 thin films acting as a host material. The films, with a columnar structure and open pores, were prepared by electron evaporation at glancing angles (GAPVD). The open porosity of the films has been estimated by measuring a water adsorption isotherm with a quartz crystal monitor. TMPyP molecules were infiltrated in the host thin films by their immersion into water solutions at controlled values of pH. The state of the adsorbed molecules, the infiltration efficiency, and the adsorption kinetics were assessed by analyzing the optical response of the films by UV-vis absorption and fluorescence techniques. The infiltration efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) developed for colloidal oxides. By a quantitative evaluation based on the analysis of the UV spectra, the infiltration process has been described by a Langmuir type adsorption isotherm and an Elovich-like kinetics. The accessibility of the infiltrated molecules in the TMPyP/TiO2 composite films is assessed by following the changes of their optical properties when exposed to the acid vapors and their subsequent recovery with time.


Marzo, 2010 | DOI: 10.1021/am900746q

Evaluation of Different Dielectric Barrier Discharge Plasma Configurations As an Alternative Technology for Green C-1 Chemistry in the Carbon Dioxide Reforming of Methane and the Direct Decomposition of Methanol


Rico, VJ; Hueso, JL; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physical Chemistry A, 114 (2010) 4009-4016

ABSTRACT

Carbon dioxide reforming of methane and direct decomposition of methanol have been investigated using dielectric harrier discharges (DBD)) at atmospheric pressure and reduced working temperatures. Two different plasma reactor configurations are compared and especial attention is paid to the influence of the surface roughness of the electrodes oil the conversion yields in the first plasma device. The influence of different filling gap dielectric materials (i.e., Al2O3 of BaTiO3) in the second packed configuration has been also evaluated. Depending on the experimental conditions of applied voltage, residence time of reactants. feed ratios, or factor configuration. different conversion yields are achieved ranging front 20 to 80% in the case of methane and 7-45% for the carbon dioxide. The direct decomposition of methanol reaches 60-100% Under similar experimental conditions. Interestingly, the selectivity toward the production of hydrogen and carbon monoxide is kept almost constant under all the experimental conditions, and the formation of longer hydrocarbon chains of coke is a byproduct is not detected. The maximum efficiency yields are observed for the packed-bed reactor configuration containing alumina for both reaction processes (similar to 1 mol H-2 per kilowatt hour for dry reforming of methane and similar to 4.5 mol H-2, per kilowatt hour for direct decomposition of methanol).


Marzo, 2010 | DOI: 10.1021/jp100346q

Morphological evolution of pulsed laser deposited ZrO2 thin films


Alvarez, R; Palmero, A; Prieto-Lopez, LO; Yubero, F; Cotrino, J; de la Cruz, W; Rudolph, H; Habraken, FHPM; Gonzalez-Elipe, AR
Journal of Applied Physics, 107 (2010) 54311-54320

ABSTRACT

Morphological evolution of ZrO2 thin films deposited during pulsed laser deposition of Zr in O-2 atmosphere has been experimentally studied at two different film deposition temperatures, 300 and 873 K. The roughness exponent, alpha, the growth exponent, beta, the coarsening exponent, 1/z, and the exponent defining the evolution of the characteristic wavelength of the surface, p, for depositions at 300 K amounted to beta = 1.0 +/- 0.1, alpha = 0.4 +/- 0.1, 1/z = 0.34 +/- 0.03, and p = 0.49 +/- 0.03, whereas for depositions carried out at 873 K amounted to beta = 0.3 +/- 0.3, alpha = 0.4 +/- 0.2, and 1/z = 0.0 +/- 0.2. Experimental error becomes important due to the flat morphology of the films inherent to the deposition technique. The change in the surface topography with the film temperature has been studied with the help of a simple Monte Carlo model which indicates the existence of two different growth regimes: a shadowing dominated growth, occurring at low temperatures, characterized by calculated values beta = 1.00 +/- 0.04, alpha = 0.50 +/- 0.04, p = 0.46 +/- 0.01, and 1/z = 0.35 +/- 0.02 and a diffusion dominated growth that takes place at high temperatures as well as at low deposition rates, characterized by calculated values beta = 0.15 +/- 0.08, alpha = 0.33 +/- 0.04, and 1/z = 0.33 +/- 0.07. The good agreement obtained between the experimental and simulated parameters is discussed within the frame of the general characteristics of the deposition method.


Marzo, 2010 | DOI: 10.1063/1.3318604

Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles


Guerrero, E; Munoz-Marquez, MA; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Journal of Applied Physics, 107 (2010) 064303-064309

ABSTRACT

In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine-capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system.


Marzo, 2010 | DOI: 10.1063/1.3327414

Oxidation State and Local Structure of Ti-Based Additives in the Reactive Hydride Composite 2LiBH(4) + MgH2


Deprez, E; Muñoz-Marquez, MA; Roldan, MA; Prestipino, C; Palomares, FJ; Minella, CB; Bosenberg, U; Dornheim, M; Bormann, R; Fernandez, A
Journal of Physical Chemistry C, 114 (2010) 3309-3317

ABSTRACT

Nowadays, the technological utilization of reactive hydride composites (RHC) Lis hydrogen storage materials is limited by their reaction kinetics. However, addition of transition-metal-based additives, for instance titanium isopropoxide (Ti-iso), to the 2LiBH(4)+MgH2 system, results in a significant improvement of sorption kinetics. In this work, the evolution of chemical state and local structure of the Ti-based additive has been investigated by means of X-ray absorption (XAS) and photoemission (XPS) spectroscopy. X-ray absorption near-edge Structure (XANES) its well as extended X-ray absorption fine structure (EXAFS) analysis have been Undertaken at the Ti K-edge. The measurements reveal the formation of a highly dispersed and disordered TiO2-like phase during ball milling. During first desorption reduced titanium oxide and titanium boride are formed and remain stable upon cycling. The Surface analysis performed by XPS shows that the reduction processes of the Ti-based additive during first desorption IS Coupled to the migration of the Ti species front the surface to the bulk of the material. Several factors, related to favoring heterogeneous nucleation of MgB2 and the increase of interfacial area through grain refinement are proposed as potential driving force, among other effects, for the observed kinetic improvement.


Febrero, 2010 | DOI: 10.1021/jp910955r

Air- and Light-Stable Superhydrophobic Colored Surfaces Based on Supported Organic Nanowires


Borras, A; Groning, P; Sanchez-Valencia, JR; Barranco, A; Espinos, JP; Gonzalez-Elipe, AR
Langmuir, 26 (2010) 1487-1492

ABSTRACT

In this work, we report oil it new type of superhydrophobic material consisting of supported organic nanowires prepared by vacuum deposition, Different intensely colored surfaces with water contact angles its high its 180 degrees call be Fabricated depending oil the composition. morphology, and density of the nanowires. These surfaces are stable in air and under intense light irradiation. The wettability properties of coatings made of metalloporphyrins and metallophthalocyanines nanowires as well as other heterostructured binary and open core@shell nanowires are studied.


Febrero, 2010 | DOI: 10.1021/la903701j

Determination of the decay rate constant for hepatocytes immobilized in alginate microcapsules


Leal-Egana, A; Diaz-Cuenca, A; Bader, A
Journal of Micoencapsulation, 27 (2010) 86-93

ABSTRACT

Primary mouse hepatocytes (between 10-250 cells per capsule) were immobilized within 1.0% w/v alginate microbeads. The textural properties of the alginate matrix were characterized and a full protocol based upon the measurement of the initial rate of Resazurin reduction was studied and standardized. Using this method, the decay rate constant (K-d = 0.45 +/- 0.01 days(-1)) and the time in which the cell viability decreases in half (VI50 = 37 +/- 0.7 h) have been measured. The method was compared with the analysis of cell vitality using Calcein A/M and Ethidium Homodimer I. Differences between the two methods were found in the viability profile due to the significant presence of double stained cells along the culture time. According to the author's knowledge, this is the first report of a systematic study and determination of the K-d value for immobilized hepatocytes, incorporating a wide range of cell concentrations within the alginate matrix.


Enero, 2010 | DOI: 10.3109/02652040903050550

Synthesis, characterization, and photoactivity of InTaO4 and In0.9Ni0.1TaO4 thin films prepared by electron evaporation


Rico, VJ; Frutos, F; Yubero, F; Espinos, JP; Gonzales-Elipe, AR
Journal of Vacuum Science & Technology A, 28 (2010) 127-134

ABSTRACT

InTaO4 and In0.9Ni0.1TaO4 thin films have been prepared by electron evaporation of successive layers of the single oxide components and posterior annealing at T > 800 degrees C. The annealed thin films presented the monoclinic crystallographic structure typical of these mixed oxides. The electrical and optical behaviors of the films, assessed by C-V measurements, surface conductivity as a function of temperature, and UV-vis absorption spectroscopy, indicate that these oxides are wide band gap semiconductors with a variable dielectric constant depending on the annealing conditions. By reflection electron energy loss spectroscopy some electronic states have been found in the gap at an energy that is compatible with the activation energy deduced from the conductivity versus 1/T plots for these oxides. The photoactivity of these materials has been assessed by looking to the evolution of the wetting contact angle as a function of the irradiation time. All the films became superhydrophilic when irradiated with UV light, while the In0.9Ni0.1TaO4 thin films also presented a small partial decrease in wetting angle when irradiated with visible photons.


Enero, 2010 | DOI: 10.1116/1.3273597



2009


Thermogravimetric and in situ SEM characterisation of the oxidation phenomena of protective nanocomposite nitride films deposited on steel


Mege-Revil, A; Steyer, P; Thollet, G; Chiriac, R; Sigala, C; Sanchez-Lopez, JC; Esnouf, C
Surface and Interface Analysis, 204 (2009) 893-901

ABSTRACT

The lifetime of TiN coatings is often limited by its poor resistance to high temperatures. For an optimized addition of silicon, both mechanical and physico-chemical properties are enhanced, owing to the formation of a nanocomposite structure. In this study, pure Ti and TiSi (80/20) targets were arc-evaporated to produce hard, single-layered coatings. Magnetron sputtered SiNx films were also synthesized for a comparison purpose. The nanocomposite structure was determined by XRD and TEM, and its efficiency regarding the mechanical properties was confirmed by nanohardness measurements. Through thermogravimetric experiments it is shown that in isothermal and dynamic conditions, the chemical stability inherent to SiNx controls the oxidation behaviour of TiSiN. However, in thermal cycling conditions TiSiN withstand efficiently temperature variations whereas SiNx does not. The aim of this study is to understand the role of SiNx on the oxidation of the TiSiN nanocomposite film. For this purpose, an in situ approach of the oxidation phenomena is detailed, based on experiments performed in an environmental scanning electron microscope (ESEM) operating in controlled pressure mode up to 1000 °C. ESEM, used in real-time oxidative conditions, has been proved to be an efficient tool to characterise the mechanism of degradation. The successive steps of the attack throughout the in situ oxidation process are as follow: oxidation first initiates at coating defects (open pores and droplets), then spreads to the whole surface. The whole flaking of the film that is observed at the microscopic scale during the cooling step proves the poor thermal fatigue resistance of SiNx. This strong propensity to cracking is explained on the basis of thermo-mechanical considerations. The nanocomposite structure thus combines the chemical stability inherent to the SiNx matrix with the beneficial thermo-mechanical properties associated to TiN nanograins.


Diciembre, 2009 | DOI: 10.1016/j.surfcoat.2009.06.040

Metal carbide/amorphous C-based nanocomposite coatings for tribological applications


Sanchez-Lopez, JC; Martinez-Martinez, D; Abad, MD; Fernandez, A
Surface and Coatings Technology, 204 (2009) 947-954

ABSTRACT

This paper tries to assess the factors governing the tribological behaviour of different nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS) and Raman spectroscopy techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the fraction of C atoms in the amorphous phase (xa-C) is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, WC/a-C, TiBC/a-C) is done and conclusions are obtained concerning the friction and wear mechanism involved.


Diciembre, 2009 | DOI: 10.1016/j.surfcoat.2009.05.038

Hybrid catalytic-DBD plasma reactor for the production of hydrogen and preferential CO oxidation (CO-PROX) at reduced temperatures


Rico, VJ; Hueso, JL; Cotrino, J; Gallardo, V; Sarmiento, B; Brey, JJ; Gonzalez-Elipe, AR
Chemical Communications, 41 (2009) 6192-6194

ABSTRACT

Dielectric Barrier Discharges (DBD) operated at atmospheric pressure and working at reduced temperatures (T < 115 °C) and a copper–manganese oxide catalyst are combined for the direct decomposition and the steam reforming of methanol (SRM) for hydrogen production and for the preferential oxidation of CO (CO-PROX)


Noviembre, 2009 | DOI: 10.1039/b909488a

Bonding Structure and Mechanical Properties of Ti-B-C Coatings


Abad, MD; Caceres, D; Pogozhev, YS; Shtansky, DV; Sanchez-Lopez, JC
Plasma Processes and Polymers, 6 (2009) S107-S112

ABSTRACT

Nanocomposite coatings combining hard phases (TiB2, TiC) with an amorphous carbon (a-C) were developed to provide a good compromise between mechanical and tribological properties for M2 steels used in a wide variety of applications such as cutting tools, bearings and gear mechanisms. A combined d.c.-pulsed and r.f.-magnetron deposition process was used to deposit nanocomposite TiBC/a-C coatings with a variable content of carbon matrix phase. Chemical composition was determined by electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) revealed that the coatings microstructure is rather amorphous with small nanocrystals of TiC and/or TiB2 (not possible to differentiate by diffraction techniques). Investigation of the chemical bonding environment by XPS and EELS allows us to confirm the presence of titanium-boron and titanium-carbon bonds together with free a-C. Coatings exhibited hardness values (H) of 25–29 GPa, effective Young modulus (E*) of 310–350 GPa, H/E* ratios over 0.080 and resistance to plastic deformation (H3/E*2) from 0.15 to 0.20. Tribological properties of the coatings were characterized by a pin-on-disk tribometer using steel and WC balls at high contact stresses (1.1 and 1.4 GPa respectively). Friction coefficients were reduced from 0.6 to 0.2 by increasing the content of free carbon without reduction of the hardness (around 28 GPa), by self-lubricant effects. The tribo-mechanical data are revised according to the phase composition and chemical bonding inside the nanocomposites.


Noviembre, 2009 | DOI: 10.1002/ppap.200930403

Manganese and iron oxides as combustion catalysts of volatile organic compounds


Duran, FG; Barbero, BP; Cadus, LE; Rojas, C; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 92 (2009) 194-201

ABSTRACT

FeMn mixed oxides were prepared by the citrate method with Fe:Mn atomic ratio equal to 1:1, 1:3 and 3:1. The sample was characterized by means of specific surface area measurements, X-ray diffractometry (XRD), temperature programmed desorption of oxygen (O2-DTP), temperature programmed reduction (TPR), X-ray fluorescence (XRF), transmission electron microscopy (TEM and SAED) and high resolution TEM (HREM). The characterization results demonstrated the formation of a Mn2O3–Fe2O3 solid solution. The catalytic performance in ethanol, ethyl acetate and toluene total oxidation on these samples was better than on Fe2O3 and Mn2O3 pure oxides.


Octubre, 2009 | DOI: 10.1016/j.apcatb.2009.07.010

Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films


Godinho, V; Denisov, VN; Mavrin, BN; Novikova, NN; Vinogradov, EA; Yakovlev, VA; Fernandez-Ramos, C; de Haro, MCJ; Fernandez, A
Applied Surface Science

ABSTRACT

Vibrational (infrared and Raman) spectroscopy has been used to characterize SiOxNy and SiOx films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiOxNy films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.


Octubre, 2009 | DOI: 10.1016/j.apsusc.2009.07.101

Formation of Nitrogen Functional Groups on Plasma Treated DLC


Lopez-Santos, C; Yubero, F; Cotrino, J; Contreras, L; Barranco, A; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 6 (2009) 555-565

ABSTRACT

Diamond like carbon (DLC) thin films have been exposed to different nitrogen containing plasmas. A dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at low pressure using N2 and mixtures Ar + NH3 have been compared. Optical Emission and X-ray Photoelectron spectroscopies, Atomic Force Microscopy and contact angle measurements have been used for this study. A DBD with Ar + NH3 is the most efficient method for DLC functionalization. Films treated with this plasma presented the highest concentration of amine groups as determined by derivatization with 4-chlorobenzaldehyde. All the treated samples underwent a significant aging with time. The efficiency of the different plasmas for DLC functionalization is discussed in the light of the intermediate species detected in the plasma.


Septiembre, 2009 | DOI: 10.1002/ppap.200900019

Incorporation and Thermal Evolution of Rhodamine 6G Dye Molecules Adsorbed in Porous Columnar Optical SiO2 Thin Films


Sanchez-Valencia, JR; Blaszczyk-Lezak, I; Espinos, JP; Hamad, S; Gonzalez-Elipe, AR; Barranco, A
Langmuir, 25 (2009) 6869-6874

ABSTRACT

Rhodamine 6G (Rh6G) dye molecules have been incorporated into transparent and porous SiO2 thin films prepared by evaporation at glancing angles. The porosity of these films has been assessed by analyzing their water adsorption isotherms measured for the films deposited on a quartz crystal monitor. Composite Rh6G/SiO2 thin films were prepared by immersion of a SiO2 thin film into a solution of the dye at a given pH. It is found that the amount of Rh6G molecules incorporated into the film is directly dependent on the pH of the solution and can be accounted for by a model based on the point of zero charge (PZC) concepts originally developed for colloidal oxides. At low pHs, the dye molecules incorporate in the form of monomers, while dimers or higher aggregates are formed if the pH increases. Depending on the actual preparation and treatment conditions, they also exhibit high relative fluorescence efficiency. The thermal stability of the composite films has been also investigated by characterizing their optical behavior after heating in an Ar atmosphere at increasing temperatures up to 275 °C. Heating induces a progressive loss of active dye molecules, a change in their agglomeration state, and an increment in their relative fluorescence efficiency. The obtained Rh6G/SiO2 composite thin films did not disperse the light and therefore can be used for integration into optical and photonic devices.


Agosto, 2009 | DOI: 10.1021/la900695t

Chemical and electronic interface structure of spray pyrolysis deposited undoped and Al-doped ZnO thin films on a commercial Cz-Si solar cell substrate


Gabas, M; Barrett, NT; Ramos-Barrado, JR; Gota, S; Rojas, TC; Lopez-Escalante, MC
Solar Energy Materials and Solar Cells, 93 (2009) 1356-1365

ABSTRACT

We have studied differences in the interface between undoped and Al-doped ZnO thin films deposited on commercial Si solar cell substrates. The undoped ZnO film is significantly thicker than the Al-doped film for the same deposition time. An extended silicate-like interface is present in both samples. Transmission electron microscopy (TEM) and photoelectron spectroscopy (PES) probe the presence of a zinc silicate and several Si oxides in both cases. Although Al doping improves the conductivity of ZnO, we present evidence for Al segregation at the interface during deposition on the Si substrate and suggest the presence of considerable fixed charge near the oxidized Si interface layer. The induced distortion in the valence band, compared to that of undoped ZnO, could be responsible for considerable reduction in the solar cell performance.


Agosto, 2009 | DOI: 10.1016/j.solmat.2009.02.018

Identification of hydrogen and deuterium at the surface of water ice by reflection electron energy loss spectroscopy


Yubero, F; Tokesi, K
Applied Physics Letters, 95 (2009) 084101

ABSTRACT

A nondestructive method to distinguish between hydrogen (H) and deuterium (D) at surfaces by reflection electron energy loss spectroscopy is presented. It is based on the analysis of the energy distributions of electrons elastically backscattered from surfaces containing H or D. We consider standard and deuterated water ices as test surfaces. The recoil energy of the backscattered electrons depends on the atomic mass of the targets, and the contributions of H, D, and O to the measured spectra can be easily separated. The results of Monte Carlo simulations corroborate the experimental findings.


Agosto, 2009 | DOI: 10.1063/1.3202402

Near-ambient X-ray photoemission spectroscopy and kinetic approach to the mechanism of carbon monoxide oxidation over lanthanum substituted cobaltites


Hueso, JL; Martinez-Martinez, D; Caballero, A; Gonzalez-Elipe, AR; Mun, BS; Salmeron, M
Catalysis Communications, 10 (2009) 1898-1902

ABSTRACT

We have studied the oxidation of carbon monoxide over a lanthanum substituted perovskite (La0.5Sr0.5CoO3−d) catalyst prepared by spray pyrolysis. Under the assumption of a first-order kinetics mechanism for CO, it has been found that the activation energy barrier of the reaction changes from ∼80 to ∼40 kJ mol−1 at a threshold temperature of ca. 320 °C. In situ XPS near-ambient pressure (∼0.2 torr) shows that the gas phase oxygen concentration over the sample decreases sharply at ca. 300 °C. These two observations suggest that the oxidation of CO undergoes a change of mechanism at temperatures higher than 300 °C.


Agosto, 2009 | DOI: 10.1016/j.catcom.2009.06.022

Comparative investigation of TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings deposited by sputtering of МАХ-phase Ti2 − хCrхAlC targets


Shtansky, DV; Kiryukhantsev-Korneev, PV; Sheveyko, AN; Mavrin, BN; Rojas, C; Fernandez, A; Levashov, EA
Surface and Coatings Technology, 203 (2009) 3595-3609

ABSTRACT

A comparative investigation of the structure and properties of TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings deposited by sputtering of МАХ-phase Ti2 − хCrхAlC targets (where x = 0, 0.5, 1.5, and 2) in an Ar atmosphere or in a gaseous mixture of Ar + N2 is presented. The coatings were characterized in terms of their structure, elemental and phase composition, hardness, elastic modulus, elastic recovery, thermal stability, friction coefficient, wear rate, corrosion, and high-temperature oxidation resistance. The structure of the coatings was studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum or in air at temperatures 600–1200 °C. The results obtained show that the TiAlCN coatings possess high hardness of 32–35 GPa, low friction coefficient against WC–Co well below 0.25, high thermal stability up to 1200 °C, and superior performance in dry milling tests against high Cr steel. Meanwhile, the coatings with high Cr content demonstrated improved oxidation resistance up to 1000 °C and superior electrochemical behavior, but their mechanical and tribological properties were deteriorated.


Agosto, 2009 | DOI: 10.1016/j.surfcoat.2009.05.036

Chemical State of Nitrogen and Visible Surface and Schottky Barrier Driven Photoactivities of N-Doped TiO2 Thin Films


Romero-Gomez, P; Rico, V; Borras, A; Barranco, A; Espinos, JP; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 113 (2009) 13341-13351

ABSTRACT

N-doped TiO2 thin films have been prepared by plasma enhanced chemical vapor deposition and by physical vapor deposition by adding nitrogen or ammonia to the gas phase. Different sets of N-doped TiO2 thin films have been obtained by changing the preparation conditions during the deposition. The samples have been characterized by X-ray diffraction, Raman, UV−vis spectroscopy, and X-ray photoemission spectroscopy (XPS). By changing the preparation conditions, different structures, microstructures, and degrees and types of doping have been obtained and some relationships have been established between these film properties and their visible light photoactivity. The N1s XP spectra of the samples are characterized by three main features, one tentatively attributed to Ti−N (i.e., nitride with a binding energy (BE) of 396.1 eV) and two others with BEs of 399.3 and 400.7 eV, tentatively attributed to nitrogen bonded simultaneously to titanium and oxygen atoms (i.e., Ti−N−O like species). By controlling the deposition conditions it is possible to prepare samples with only one of these species as majority component. It has been shown that only the samples with Ti−N−O like species show surface photoactivity being able to change their wetting angle when they are illuminated with visible light. The presence of these species and an additional complex structure formed by a mixture of anatase and rutile phases is an additional condition that is fulfilled by the thin films that also present photocatalytic activity with visible light (i.e., surface and Schottky barrier driven photoactivities). The relationships existing between the reduction state of the samples and the formation of Ti−N or Ti−N−O like species are also discussed.


Julio, 2009 | DOI: 10.1021/jp9024816

Nanoindentation of TiO2 thin films with different microstructures


Gaillard, Y; Rico, VJ; Jimenez-Pique, E; Gonzalez-Elipe, AR
Journal of Physics D: Applied Physics, 42 (2009) 145305

ABSTRACT

A series of nanoindentation tests has been carried out with TiO2 films produced by physical vapour deposition (PVD) under different conditions. Films with different microstructures and crystallographic structures have been prepared by changing experimental parameters such as the temperature of the substrate, the deposition angle (by the so-called glancing angle physical vapour deposition, GAPVD) or by exposing the growing film to a beam of accelerated ions. The obtained results of hardness and Young's modulus depict interesting correlations with the microstructure and structure of the films providing a general picture for the relationships between these characteristics and their mechanical properties. Different models have been used to extract Young's modulus and hardness parameters from the experimental nanoindentation curves. The obtained results are critically discussed to ascertain the ranges of validity of each procedure according to the type of sample investigated.


Julio, 2009 | DOI: 10.1088/0022-3727/42/14/145305

Electrical characteristics of mixed Zr–Si oxide thin films prepared by ion beam induced chemical vapor deposition at room temperature


Ferrer, FJ; Frutos, F; Garcia-Lopez, J; Jimenez, C; Yubero, F
Thin Solid Films, 517 (2009) 5446-5452

ABSTRACT

Mixed Zr–Si oxide thin films have been prepared at room temperature by ion beam decomposition of organometallic volatile precursors. The films were flat and amorphous. They did not present phase segregation of the pure single oxides. A significant amount of impurities (–C–, –CHx, –OH, and other radicals coming from partially decomposed precursors) remained incorporated in the films after the deposition process. This effect is minimized if the Ar content in the O2/Ar bombarding gas is maximized. Static permittivity and breakdown electrical field of the films were determined by capacitance–voltage and current–voltage electrical measurements. It is found that the static permittivity increases non-linearly from ~ 4 for pure SiO2 to ~ 15 for pure ZrO2. Most of the dielectric failures in the films were due to extrinsic breakdown failures. The maximum breakdown electrical field decreases from ~ 10.5 MV/cm for pure SiO2 to ~ 45 MV/cm for pure ZrO2. These characteristics are justified by high impurity content of the thin films. In addition, the analysis of the conduction mechanisms in the formed dielectrics is consistent to Schottky and Poole-Frenkel emission for low and high electric fields applied, respectively.


Julio, 2009 | DOI: 10.1016/j.tsf.2009.01.099

Growth of Crystalline TiO2 by Plasma Enhanced Chemical Vapor Deposition


Borras, A; Sanchez-Valencia, JR; Widmer, R; Rico, VJ; Justo, A; Gonzalez-Elipe, AR
Crystal Growth & Design, 9 (2009) 2868-2876

ABSTRACT

TiO2 thin films in the form of anatase have been prepared by plasma enhanced chemical vapor deposition (PECVD) at 523 K as the substrate temperature and a low working pressure. The study of the microstructure and texture of the films at different stages of deposition show that their growth follows the Kolmogorov’s model developed to describe the evolution of crystalline films from a saturated homogeneous medium. An additional characteristic feature of the growth process by PECVD is the formation of different crystalline domains, particularly at low deposition rates. The effects of this parameter and of the characteristics of the substrate on the growing process are also addressed.


Junio, 2009 | DOI: 10.1021/cg9001779

Thermal Evolution of WC/C Nanostructured Coatings by Raman and In Situ XRD Analysis


El Mrabet, S; Abad, MD; Lopez-Cartes, C; Martinez-Martinez, D; Sanchez-Lopez, JC
Plasma Processes and Polymers, 6 (2009) S444-S449

ABSTRACT

In this work, a series of WC/C nanostructured films were deposited on silicon substrates by changing the ratio of sputtering power applied to graphite and WC magnetron sources (PC/PWC: 0, 0.1, 0.5, 1). The thermal stability of WC/C coatings was followed in situ by means of X-ray diffraction measurements up to 1 100 °C in vacuum (10−1 Pa). Initially, the film microstructure is composed of nanocrystalline WC1−x and W2C phases. As the PC/PWC ratio increases the crystallinity decreases, and WC1−x becomes the predominant phase from PC/PWC = 0.1. The results show that the structural evolution with temperature of all studied layers depends essentially on their initial phase and chemical composition (determined by the synthesis conditions: ratio PC/PWC). The coating deposited at PC/PWC = 0 reveals a transformation of W2C phase into W and W3C phases at 400 °C. However, the samples with PC/PWC greater than 0 exhibits an improved thermal stability up to 600–700 °C where the WC1−x begins to transform into W2C and WC phases. At 900 °C, WC is the predominant phase, especially for those coatings prepared with higher ratios. Further annealing above 1 000 °C yields W as the foremost phase. The thermal behaviour was later studied by means of Raman spectroscopy measurements at certain temperatures where the main changes in phase composition were observed. Particularly, a fitting analysis was carried out on the D and G bands typical of disordered and amorphous carbon. The changes induced during heating are discussed in terms of the positions of D and G lines, and full width at half maximum (FWHM).


Junio, 2009 | DOI: 10.1002/ppap.200931004

Application of 29Si and 27Al MAS NMR Spectroscopy to the Study of the Reaction Mechanism of Kaolinite to Illite/Muscovite


Mantovani, M; Escudero, A; Becerro, AI
Clays and Clay Minerals, 57 (2009) 302-310

ABSTRACT

Understanding the mechanisms for illitization of clay minerals has important applications in reconstructing geologic histories and determining the origins of physical and chemical characteristics of buried sediments. While many studies have been carried out on this topic, few have focused on the mechanism of illite formation from kaolinite. The purpose of this study was to investigate more deeply the illitization of kaolinite in KOH solution at a high solid/liquid ratio (1000 mg/mL). X-ray diffraction (XRD) and infrared spectroscopy were used to follow the formation of new crystalline phases and the composition of the octahedral sheet, while the transformation of the Si and Al local environments was analyzed by 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The results revealed that the first reaction stage consists of the diffusion of Al from the octahedral to the tetrahedral sheet of the kaolinite TO layers, giving rise to the precursors of the illite/muscovite nuclei. Combination of XRD with 27Al MAS NMR measurements indicated that a minimum amount of tetrahedral Al is required in the original TO layer before condensation of a second tetrahedral sheet occurs to complete the formation of the illite/muscovite TOT layers.


Junio, 2009 | DOI: 10.1346/CCMN.2009.0570303

Thermal Stability and Oxidation Resistance of Nanocomposite TiC/a-C Protective Coatings


Martinez-Martinez, D; Lopez-Cartes, C; Gago, R; Fernandez, A; Sanchez-Lopez, JC
Plasma Processes and Polymers, 6 (2009) S462-S467

ABSTRACT

Nanocomposite films composed by small crystallites of hard phases embedded in an amorphous lubricant matrix have been extensively studied as protective coatings. These kinds of coatings have often to work in extreme environments, exposed to high temperatures (above 800–900 °C), and/or oxidizing/corrosive atmospheres, which may resist. As a result, it is important to study the behavior of such coatings at high temperatures (thermal stability) and in the presence of oxygen (oxidation resistance). In this sense, we have selected a TiC/a-C nanocomposite coating with good mechanical and tribological properties in order to do several thermal tests under three different environments: high vacuum (10−6 mbar), low vacuum (10−1 mbar), and air. Our observations allow us to establish that the film microstructure is stable at least up to 1 000 °C in high vacuum. When oxygen is present, the practical temperature of use is reduced at 700 °C (low partial pressure) and 300 °C (air) by formation of Ti oxides and C removal.


Mayo, 2009 | DOI: 10.1002/ppap.200931002

Wetting angles and photocatalytic activities of illuminated TiO2 thin films


Rico, V; Romero, P; Hueso, JL; Espinos, JP; Gonzalez-Elipe, AR
Catalysis Today, 143 (2009) 347-354

ABSTRACT

TiO2 thin films have been prepared by physical vapour deposition (PVD) and plasma enhanced chemical vapour deposition (PECVD) to study the UV-induced photo-activity of this material. Wetting angle variations and photo-catalytic activity for the degradation of dyes upon UV illumination have been compared for thin films with different crystalline structure (amorphous, rutile and anatase), microstructure (columnar, compact, etc.) and porosities as estimated from the values of their refraction indices and their direct assessment with a quartz crystal monitor. The surface of the thin films became superhydrophilic upon UV light irradiation and then it recovered its original state by keeping the samples in the dark. Wetting angle decays follow very similar kinetics for amorphous and crystalline films, independently of their actual porosities. By contrast the photo-catalytic activity was very dependent on the crystalline structure of the films (anatase > rutile > amorphous) and on their porosities. The different behaviour depicted by the films with regard to these two properties suggests that they respond to different though related mechanisms and that they cannot be considered as equivalent when trying to prove the photo-activity of TiO2.


Mayo, 2009 | DOI: 10.1016/j.cattod.2008.09.037

High deposition rates of uniform films in tetramethylsilane-based plasmas generated by elementary microwave sources in matrix configuration


Latrasse, L; Lacoste, A; Sanchez-Lopez, JC; Bes, A; Rayar, M; Pelletier, J
Surface and Coatings Technology, 203 (2009) 2343-2349

ABSTRACT

Plasma scaling up can be achieved by distributing elementary microwave plasma sources on planar rectangular networks. These so-called matrix plasmas can generate uniform sheets of plasma over a wide argon pressure range, from 7.5 to 750 Pa, with densities between 1012 and 1013 cm− 3. In order to estimate the capabilities of matrix plasmas for PACVD processing in terms of deposition rate and uniformity, SiOCH and SiNCH films were deposited using TMS (tetramethylsilane), as the organic gas precursor of silicon, mixed with oxygen or nitrogen flows. Plasmas of O2 / TMS and N2 / TMS gas mixtures can be sustained between 5 and 25 Pa. Variations in the deposition rate as a function of microwave power and nitrogen partial pressure are reported. Thickness uniformity of SiOCH and SiNCH films was measured across a silicon wafer. The obtained deposition rates exceed 1.3 μm/min and the films present a uniformity better than 5% on 75 mm diameter silicon wafers. Composition of the films has also been analyzed by XPS as a function of process parameters: microwave input power, composition of gas mixture, and N2 partial pressure. In particular, these analyses have shown a very low yield of nitrogen incorporation when using N2 gas as nitrogen precursor and high Si and Si–Si bonding contents in the films, probably due to a strong fragmentation of the TMS precursor in the high density plasma.


Mayo, 2009 | DOI: 10.1016/j.surfcoat.2009.02.121

Molecular dynamics simulation of the effect of pH on the adsorption of rhodamine laser dyes on TiO2 hydroxylated surfaces


Hamad, S; Sanchez-Valencia, JR; Barranco, A; Mejias, JA; Gonzalez-Elipe, AR
Molecular Simulation, 35 (2009) 1140-1151

ABSTRACT

We have carried out a study of adsorption, on the (1 0 1) surface of anatase TiO2, of two industrially relevant rhodamine molecules [rhodamine 6G (R6G) and rhodamine 800 (R800)] employing molecular dynamics. These theoretical studies have shown that R6G must adsorb on surfaces under basic conditions. Moreover, the adsorption of this molecule shows a strong dependence upon the pH of the system, i.e. under basic conditions the adsorption energy is quite high, under neutral conditions the adsorption energy is lower and under acidic conditions an even lower adsorption energy indicates that there must be very little adsorption under such conditions. By contrast, for R800, there is little dependence of the adsorption energy upon the pH, suggesting that the amount of adsorption of these molecules is little affected by this parameter. These theoretical results are in qualitative agreement with the experimental results consisting of the incorporation of these dye molecules into porous thin films.


Mayo, 2009 | DOI: 10.1080/08927020903108083

Surface nanostructuring of TiO2 thin films by ion beam irradiation


Romero-Gomez, P; Palmero, A; Yubero, F; Vinnichenko, M; Kolitsch, A; Gonzalez-Elipe, AR
Scripta Materialia, 60 (2009) 574-577

ABSTRACT

This work reports a procedure to modify the surface nanostructure of TiO2 anatase thin films through ion beam irradiation with energies in the keV range. Irradiation with N+ ions leads to the formation of a layer with voids at a depth similar to the ion-projected range. By setting the ion-projected range a few tens of nanometers below the surface of the film, well-ordered nanorods appear aligned with the angle of incidence of the ion beam. Slightly different results were obtained by using heavier (S+) and lighter (B+) ions under similar conditions.


Abril, 2009 | DOI: 10.1016/j.scriptamat.2008.12.014

Properties of Ti(C,N) cermets synthesized by mechanically induced self-sustaining reaction


Cordoba, JM; Sanchez-Lopez, JC; Aviles, MA; Alcala, MD; Gotor, FJ
Journal of the European Ceramic Society, 29 (2012) 1173-1182

ABSTRACT

The properties of TiCxN1−x/(Ni or Co) cermets sintered by a pressureless method from powder mixtures, and obtained for the first time by a mechanically induced self-sustaining reaction process (MSR), were studied. The hardness, toughness, friction and wear coefficients, and oxidation resistance were determined. It was shown that cermets obtained from powdered materials synthesized in one single MSR step possessed improved mechanical properties, similar to those obtained in cermets with more complex bulk compositions. Higher wear resistances were observed in cermets whose hard phase was richer in carbon. The oxidation resistance of the cermets depended primarily on the binder composition. This resistance was better for those cermets with cobalt as the binder. Superior oxidation resistance was displayed when small amounts of W or Mo were incorporated into the binder.


Abril, 2009 | DOI: 10.1016/j.jeurceramsoc.2008.08.019

Tribological carbon-based coatings: An AFM and LFM study


Martinez-Martinez, D; Kolodziejczyk, L; Sanchez-Lopez, JC; Fernandez, A
Surface Science, 603 (2009) 973-979

ABSTRACT

In this work some carbon-based coatings were studied by atomic force microscopy (AFM) and lateral force microscopy (LFM) techniques in order to evaluate their microstructure and friction properties at the micro and nanoscale. With this aim, four samples were prepared by magnetron sputtering: an amorphous carbon film (a–C), two nanocomposites TiC/a–C with different phase ratio (∼1:1 and ∼1:3) and a nanocrystalline TiC sample. Additionally, a highly oriented pyrolytic graphite (HOPG) and an amorphous hydrogenated carbon coating (a-C:H) were included to help in the evaluation of the influence of the roughness and the hydrogen presence respectively. The topography (roughness) of the samples was studied by AFM, whereas LFM was used to measure the friction properties at the nanoscale by two different approaches. Firstly, an evaluation of possible friction contrast on the samples was done. This task was performed by subtraction of forward and reverse images and lately confirmed by the study of lateral force profiles in both directions and the histograms of the subtraction images. Secondly, an estimation of the average friction coefficient over the analysed surface of each sample was carried out. To take into account the tip evolution/damaging, mica was used as a reference before and after each sample (hereafter called sandwich method), and samples-to-mica friction ratios were calculated. The LFM was shown to be a useful tool to characterise a mixture of phases with different friction coefficients. In general, the friction ratios seemed to be dominated by the amorphous carbon phase, as it was impossible to distinguish among samples with different proportions of the amorphous phase (friction ratios between 1.5 and 1.75). Nevertheless, it could be concluded that the differences in friction behaviour arose from the chemical aspects (nature of the phase and hydrogen content) rather than surface characteristics, since the roughness (Ra values up to 5.7 nm) does not follow the observed trend. Finally, the Ogletree method was employed in order to calibrate the lateral force and estimate the friction coefficient of our samples. A good agreement was found with macroscopic and literature values going from ∼0.3 for TiC to ∼0.1 for pure carbon.


Abril, 2009 | DOI: 10.1016/j.susc.2009.01.043

Water plasmas for the revalorisation of heavy oils and cokes from petroleum refining


Hueso, JL; Rico, VJ; Cotrino, J; Jimenez-Mateos, JM; Gonzalez-Elipe, AR
Environmental Science & Technology, 43 (2009) 2557-2562

ABSTRACT

This work investigates the possibility of using plasmas to treat high boiling point and viscous liquids (HBPVL) and cokes resulting as secondary streams from the refining of oil. For their revalorisation, the use of microwave (MW) induced plasmas of water is proposed, as an alternative to more conventional processes (i.e., catalysis, pyrolysis, combustion, etc.). As a main result, this type of energetic cold plasma facilitates the conversion at room temperature of the heavy aromatic oils and cokes into linear hydrocarbons and synthesis gas, commonly defined as syngas (CO + H2 gas mixture). The exposure of the coke to this plasma also facilitates the removal of the sulfur present in the samples and leads to the formation on their surface of a sort of carbon fibers and rods network and new porous structures. Besides, optical emission measurements have provided direct evidence of the intermediates resulting from the fragmentation of the heavy oils and cokes during their exposure to the water plasma. Furthermore, the analysis of the mass spectra patterns suggests a major easiness to break the aromatic bonds mainly contained in the heavy oils. Therefore, an innovative method for the conversion of low value residues from oil-refining processes is addressed.


Marzo, 2009 | DOI: 10.1021/es900236b

Wetting Angles on Illuminated Ta2O5 Thin Films with Controlled Nanostructure


Rico, V; Borras, A; Yubero, F; Espinos, JP; Frutos, F; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 113 (2009) 3775-3784

ABSTRACT

Ta2O5 thin films with different nanostructure and surface roughness have been prepared by electron evaporation at different angles between the evaporation source and the substrates. Large variation of refraction indexes (n) from 1.40 to 1.80 were obtained by changing the geometry of evaporation and/or by annealing the evaporated films at increasing temperatures up to 1000 °C to make them crystalline. Very flat and compact thin films (n = 2.02) were also obtained by assisting the growth by bombardment with O2+ ions of 800 eV kinetic energy. A similar correlation has been found between the wetting contact angle of water and the roughness of the films for the evaporated and evaporated + annealed samples, irrespective of their procedure of preparation and other microstructural characteristics. When the films were illuminated with UV light of h > Eg = 4.2 eV (Eg, band gap energy of Ta2O5), their surface became superhydrophilic (contact angle < 10°) in a way quite similar to those reported for illuminated TiO2 thin films. The rate of transformation into the superhydrophilic state was smaller for the crystalline than for the amorphous films, suggesting that in Ta2O5 the size of crystal domains at the surface is an important parameter for the control of this kinetics. Changes in the water contact angle on films illuminated with visible light were also found when they were subjected to implantation with N2+ ions of 800 eV kinetic energy. The origin of this photoactivity is discussed in terms of the electronic band gap states associated with the nitrogen-implanted atoms. The possibility of preparing antireflective and self-cleaning coatings of Ta2O5 is discussed.


Marzo, 2009 | DOI: 10.1021/jp805708w

Growth Mechanism and Chemical Structure of Amorphous Hydrogenated Silicon Carbide (a-SiC:H) Films Formed by Remote Hydrogen Microwave Plasma CVD From a Triethylsilane Precursor: Part 1


Wrobel, AM; Walkiewicz-Pietrzykowska, A; Ahola, M; Vayrynen, IJ; Ferrer-Fernandez, FJ; Gonzalez-Elipe, AR
Chemical Vapor Deposition, 15 (2009) 39-46

ABSTRACT

Amorphous hydrogenated silicon carbide (a-SiC:H) films are produced by remote microwave hydrogen plasma (RHP)CVD using triethylsilane (TrES) as the single-source precursor. The reactivity of particular bonds of the precursor in the activation step is examined using tetraethylsilane as a model compound for the RHP-CVD experiments. The susceptibility of a TrES precursor towards film formation is characterized by determining the yield of RHP-CVD and comparing it with that of the trimethylsilane precursor. The effect of substrate temperature (Ts) on the rate of the RHP-CVD process, chemical composition, and chemical structure of the resulting a-SiC:H films is reported. The substrate temperature dependence of the film growth rate implies that film growth is independent of the temperature and RHP-CVD is a mass transport-limited process. The examination of the a-SiC:H films, performed by means of X-ray photoelectron spectroscopy (XPS), elastic recoil detection analysis (ERDA), and Fourier transform infrared absorption spectroscopy (FTIR), reveals that the increase in the substrate temperature from 30 °C to 400 °C causes the elimination of organic moieties from the film and the formation of a Si-carbidic network structure. On the basis of the results of the structural study, the chemistry involved in film formation is proposed.


Marzo, 2009 | DOI: 10.1002/cvde.200806726

Duplex SiCN/DLC coating as a solution to improve fretting—Corrosion resistance of steel


Pech, D; Schupp, N; Steyer, P; Hack, T; Gachon, Y; Heau, C; Loir, AS; Sanchez-Lopez, JC
Wear, 266 (2009) 832-838

ABSTRACT

Fretting corrosion damages are commonly observed when two metallic bodies, which are in contact with each other, are subjected to oscillatory motions of low amplitude. Such kind of degradation mode is often responsible for limited durability of aeronautical joints. In the present paper, a multifunctional duplex coating based on Si–C–N and diamond-like carbon (DLC) materials, combining corrosion resistance and good tribological properties is described. Amorphous hydrogenated SiC, SiCN, SiC/DLC and SiCN/DLC were deposited on steel substrates by a plasma assisted chemical vapour deposition (PACVD) technique, using tetramethylsilane (TMS), ammonia (NH3) or acetylene (C2H2) as gas precursors. Nitrogen incorporation has shown to improve the corrosion protection ability of SiC coatings. The corrosion behaviour and the tribological performance in aqueous media of SiCN/DLC coating have therefore been investigated. A test rig has been designed to validate the fretting resistance of this duplex coating for aeronautic applications. It was found that the combination of a SiCN-based PACVD sublayer with a DLC topcoat could provide an enhanced solution to withstand both fretting and corrosion.


Marzo, 2009 | DOI: 10.1016/j.wear.2008.12.007

Self-lubricating Ti–C–N nanocomposite coatings prepared by double magnetron sputtering


Martinez-Martinez, D; Lopez-Cartes, C; Justo, A; Fernandez, A; Sanchez-Lopez, JC
Solid State Sciences, 11 (2009) 660-670

ABSTRACT

This paper is devoted to the development of Ti(C,N)-based nanocomposite protective coatings consisting of nanocrystals of a hard phase (TiN or TiCxNy) embedded in an amorphous carbon-based matrix (a-C or a-CNx). The objective here is the achievement of a good compromise between the mechanical and tribological properties by the appropriate control of the hard/soft phase ratio and the microstructural characteristics of the film. To achieve this purpose, dual magnetron sputtering technique was employed following two different strategies. In the first one, we use Ti and graphite targets and Ar/N2 gas mixtures, while in the second case, TiN and graphite targets are sputtered in an Ar atmosphere. By changing the sputtering power applied to each magnetron, different sets of samples are prepared for each route. The effect of the bias voltage applied to the substrate is also studied in some selected cases. The mechanical and tribological properties of the films are characterized and correlated with the microstructure, crystallinity and phase composition. The establishment of correlations enables the development of advanced coatings with tailored mechanical and tribological properties for desired applications.


Marzo, 2009 | DOI: 10.1016/j.solidstatesciences.2008.10.017

Study by grazing incident diffraction and surface spectroscopy of amalgams from ancient mirrors


Herrera, LK; Duran, A; Franquelo, ML; Gonzalez-Elipe, AR; Espinos, JP; Rubio-Zuazo, J; Castro, GR; Justo, A; Perez-Rodriguez, JL
Central European Journal of Chemistry, 7 (2009) 47-53

ABSTRACT

Characterization of four amalgam surfaces, with different alteration degrees from Andalusia historical mirrors, has been carried out by grazing-incidence X-ray diffraction (GIXRD), and other spectroscopic techniques (SEM/EDX, XPS, and REELS). The combination of all these techniques allows determining the corrosion state of the amalgams. The results show that the amalgams are composed in all cases of a binary alloy of tin and mercury. As mercury has high vapour pressure at RT, it slowly segregates and eventually evaporates, it leaves finely divided particles of tin that easily can be oxidize, forming tin monoxide (SnO) and tin dioxide (SnO2). In one of the samples, most of the amalgam remains unoxidized, since Hg0.1Sn0.9 and metallic Sn phases are the major components; in two other samples, Hg0.1Sn0.9 and Sn phases are not detected while SnO2 and SnO phases appear. Finally, in the last studied sample, only SnO2 phase is detected. The surface analyses of these samples by XPS show that, for most of them an unique chemical species (Sn4+) is found.


Marzo, 2009 | DOI: 10.2478/s11532-008-0089-1

Fabrication of ordered crystalline zirconium nanoporous membranes by an one-step procedure


Marquez, F; Morant, C; Pirota, KR; Borras, A; Sanz, JM; Elizalde, E
Nano Today, 4 (2009) 21-26

ABSTRACT

Crystalline porous zirconium membranes were obtained by physical vapor deposition on AAO templates at room temperature. These membranes were found to have similar hexagonal nanohole arrays as the template and high crystallinity. The pore size of the synthesized metallic membranes could be controlled during the synthesis through appropriate parameters in the experimental procedure.


Febrero, 2009 | DOI: 10.1016/j.nantod.2008.10.012

Porosity and microstructure of plasma deposited TiO2 thin films


Borras, A; Sanchez-Valencia, JR; Garrido-Molinero, J; Barranco, A; Gonzalez-Elipe, AR
Microporous and Mesoporous Materials, 118 (2009) 314-324

ABSTRACT

The microstructure of TiO2 thin films prepared by plasma enhanced chemical vapour deposition has been assessed by using water adsorption–desorption isotherms measured by means of a quartz crystal monitor (QCM). Thin films have been deposited by using titanium tetraisopropoxide as a precursor and by changing different experimental parameters of the deposition procedure such as temperature of the substrate, pressure, and gas composition in the plasma. The films were characteristic of different microstructures that, according to their scanning electron micrographs, have been categorized as columnar, homogeneous and crystalline. They also have different refraction indices with values between 1.95 and 2.41. Water and toluene adsorption isotherms have been measured by means of a QCM monitor for the films heated in vacuum to remove the water previously adsorbed in their pores. The analysis of the adsorption-desorption isotherms by means of the so called “t-plots” and the determination of the pore size distribution curves rendered that the three kinds of microstructures presented different kinds of isotherms and water adsorption behaviours. Columnar films consisted of micro- and meso-pores had a very high adsorption hystheresis at low pressures. Homogeneous films only had micropores and presented no adsorption hystheresis. Crystalline films consisted of both micro- and meso-pores but had no adsorption hystheresis at low pressures. A zone scheme has been proposed to account for the microstructure of the films depending on the plasma conditions utilized. The implications of the different water adsorption behaviours of the films for the determination of their refraction indices are discussed.


Febrero, 2009 | DOI: 10.1016/j.micromeso.2008.09.002

WC/a-C nanocomposite thin films: Optical and electrical properties


Abad, MD; Sanchez-Lopez, JC; Cusnir, N; Sanjines, R
Journal of Applied Physics, 105 (2009) 033510

ABSTRACT

WC/amorphous carbon (a-C) thin films were deposited by dual magnetron sputtering from individual WC and graphite targets. The influence of film composition and microstructure on the optical and electrical properties was investigated. As evidenced by x-ray photoelectron spectroscopy and grazing angle x-ray diffraction measurements, the WC/a-C films are composite materials made of hexagonal W2C and/or cubic β-WC1−X nanocrystallites embedded in (a-C) matrix. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the van der Pauw method between 20 and 300 K. Both the optical and the electrical properties of the WC/a-C films are correlated with the chemical composition and microstructure evolution caused by a-C addition. The optical properties of W2C/a-C and β-WC1−x/a-C films with a-C content ≤ 10 at. % are explained by modeling their dielectric functions by a set of Drude–Lorentz oscillators. Further increase in a-C content leads only to the formation of β-WC1−x/a-C nanocomposite structures and their optical properties progressively evolve to those of a-C single phase. The electrical resistivity as a function of the temperature of all the films exhibits a negative temperature coefficient of resistivity. Theoretical fitting using the grain-boundary scattering model shows that the transport properties are mainly limited by the grain size and electron mean free path parameters.


Febrero, 2009 | DOI: 10.1063/1.3060717

Optically Active Luminescent Perylene Thin Films Deposited by Plasma Polymerization


Blaszczyk-Lezak, I; Aparicio, FJ; Borras, A; Barranco, A; Alvarez-Herrero, A; Fernandez-Rodriguez, M; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 113 (2009) 12840-12847

ABSTRACT

This work reports about the preparation of plasma polymerized thin films of perylene with thicknesses 30−150 nm and their characterization by different methods and the analysis of their optical properties. Highly absorbent and fluorescent films have been obtained by this method that combines the sublimation of the perylene molecules and their controlled polymerization by the interaction with remote Ar plasma. The polymeric films are very flat with a root mean square (rms) roughness in the range 0.3−0.4 nm. In contrast with the sublimated layers of perylene that present a high scattering of light, the polymerized films depict the well-defined absorption bands in the region 400−450 nm and fluorescence spectra of the perylene molecule at 475 nm. The films are formed by a matrix formed by cross-linked fragments of perylene and intact molecules that confer the observed optical properties to this material. The optical and microstructural characteristics of this type of thin films and the possibility to perform their deposition by using lithographic procedures make them suitable for their integration into photonic components for various applications. A preliminary study of the use of these films as an optical sensor of NO2 is also presented.


Enero, 2009 | DOI: http://pubs.acs.org/doi/abs/10.1021/jp807634j

Luminescent and Optical Properties of Nanocomposite Thin Films Deposited by Remote Plasma Polymerization of Rhodamine 6G


Aparicio, FJ; Borras, A; Blaszczyk-Lezak, I; Groning, P; Alvarez-Herrero, A; Fernandez-Rodriguez, M; Gonzalez-Elipe, AR; Barranco, A
Plasma Processes and Polymers, 6 (2009) 17-26

ABSTRACT

Mechanically stable and insoluble fluorescent thin films have been deposited by sublimating Rhodamine 6G laser dye in the downstream region of a low-power microwave ECR plasma using an experimental set-up designed to control the interaction of the dye molecule with the glow discharge. The use of reactive organosilane plasmas allows to control the dye distribution inside the matrix, leading to solid nanocomposite thin films containing non-aggregated dye molecules. The suppression of aggregates is a key issue to avoid fluorescence quenching. The obtained nanocomposite films are interesting because of their strong absorption and high fluorescence emission. In addition, they can be patterned using in situ plasma treatments in order to produce optically functional devices.


Enero, 2009 | DOI: 10.1002/ppap.200800092

Influence of the microstructure on the mechanical and tribological behavior of TiC/a-C nanocomposite coatings


Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Thin Solid Films, 517 (2009) 1662-1671

ABSTRACT

The performance of protective thin films is clearly influenced by their microstructure. The objective of this work is to study the influence of the structure of TiC/a-C nanocomposite coatings with a-C contents ranging from ~ 0% to 100% on their mechanical and tribological properties measured by ultramicroindentation and pin-on-disks tests at ambient air, respectively. The microstructure evolves from a polycrystalline columnar structure consisting of TiC crystals to an amorphous and dense TiC/a-C nanocomposite structure when the amount of a-C is increased. The former samples show high hardness, moderate friction and high wear rates, while the latter ones show a decrease in hardness but an improvement in tribological performance. No apparent direct correlation is found between hardness and wear rate, which is controlled by the friction coefficient. These results are compared to the literature and explained according to the different film microstructures and chemical bonding nature. The film stress has also been measured at the macro and micro levels by the curvature and Williamson–Hall methods respectively. Other mechanical properties of the coating such as resilience and toughness were evaluated by estimating the H3/E⁎2 and H/E⁎ ratios and the percentage of elastic work (We). None of these parameters showed a tendency that could explain the observed tribological results, indicating that for self-lubricant nanocomposite systems this correlation is not so simple and that the assembly of different factors must be taken into account.


Enero, 2009 | DOI: 10.1016/j.tsf.2008.09.091



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