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Steering the Self-Assembly of Octadecylamine Monolayers on Mica by Controlled Mechanical Energy Transfer from the AFM Tip

Benitez, JJ; Heredia-Guerrero, JA; Salmeron, M
Journal of Physical Chemistry C, 114 (2010) 12630-12634


We have studied the effect of mechanical energy transfer from the tip of an atomic force microscope on the dynamics of self-assembly of monolayer films of octadecylamine on mica. The formation of the self-assembled film proceeds in two successive stages, the first being a fast adsorption from solution that follows a Langmuir isotherm. The second is a slower process of island growth by aggregation of the molecules dispersed on the surface. We found that the dynamics of aggregation can be altered substantially by the addition of mechanical energy into the system through controlled tip surface interactions. This leads to both the creation of pinholes in existing islands as a consequence of vacancy concentration and to the assembly of residual molecules into more compact islands.

Julio, 2010 | DOI: 10.1021/jp102813s

Anomalous group velocity at the high energy range of a 3D photonic nanostructure

Botey, M; Martorell, J; Dorado, LA; Depine, RA; Lozano, G; Miguez, H
Optics Express, 18 (2010) 15682-15690


We report on a study of electromagnetic waves propagation in thin periodically ordered photonic nanostructures in the spectral range where the light wavelength is on the order of the lattice parameter. The vector KKR method we use allows us to determine the group index from finite photonic structures including extinction providing confirmation of recently emerged results. We show that for certain frequencies the group velocity of opal slabs can either be superluminal or approach zero depending on the crystal thickness and the unavoidable presence of losses. In some cases, group velocity can be negative. Such behavior can be clearly attributed to the finite character of the three-dimensional structure and reproduces previously reported experimental observations. Calculations show that contrary to the predictions of extraordinary group velocity reductions for infinite periodic structures, the group velocity of real opals may exhibit strong fluctuations at the high energy range. Hence, a direct identification between the calculated anomalous group velocities, for an actual opal film, and the predicted propagating low dispersion modes for an ideal infinite ordered structure seems difficult to establish.

Julio, 2010 | DOI: 10.1364/OE.18.015682

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


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

Microstructural Effects on the Creep Deformation of Alumina/Single-Wall Carbon Nanotubes Composites

Gomez-Garcia, D; Poyato, R; Lee, Z; Castillo-Rodriguez, M; Dominguez-Rodriguez, A; Radmilovic, V; Padture, NP
Journal of the American Ceramic Society, 93 (2010) 2042-2047


The enhanced high-temperature creep resistance in alumina/single-wall carbon nanotubes (SWNTs) composites has been attributed to the unprecedented grain-boundary structure of these composites, where the SWNTs bundles segregated at the alumina grain boundaries partially impede grain-boundary sliding. In this study, the effect of SWNTs distributions at alumina grain boundaries on the creep behavior of alumina/SWNTs composites has been investigated. Microstructures of two different alumina/10 vol% SWNTs composites, one with heterogeneous and the other with homogenous distributions of SWNTs at grain boundaries, have been characterized quantitatively. The steady-state creep rate (uniaxial compression) in the heterogeneous composite has been found to be over three times higher than that in the homogeneous composite at 1300° and 1350°C (argon atmosphere). It is argued that the less uniform distribution of SWNTs at the alumina grain boundaries in the heterogeneous composite results in less effective obstruction of grain-boundary sliding, and attendant higher creep rate. This also results in more efficient recovery in that composite.

Julio, 2010 | DOI: 10.1111/j.1551-2916.2010.03681.x

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


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


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


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

Porous One-Dimensional Photonic Crystal Coatings for Gas Detection

Hidalgo, N; Calvo, ME; Colodrero, S; Miguez, H
IEEE Sensors Journal, 10 (2010) 1206-1212


Herein, we present an overview of recent progress on the development of different types of porous 1-D photonic crystal coatings which are optically responsive to gas pressure changes in the environment. Modification of the surrounding vapor pressure gives rise to adsorption and condensation phenomena within the porous networks of the photonic crystal building blocks, varying their refractive index and hence their optical features. This effect can be put into practice to precisely detect and monitor changes in the ambient through the spectral shift of either the photonic bandgap of the structure or of some other optical features. Our results demonstrate the potential of these optical coatings as new materials for gas sensing devices.

Julio, 2010 | DOI: 10.1109/JSEN.2010.2043525

Gallium Arsenide Infiltration of Nanoporous Multi layers: A Route to High-Dielectric-Contrast One-Dimensional Photonic Crystals

Sanchez-Sobrado, O; Thomas, K; Povey, I; Pemble, ME; Miguez, H
Small, 6 (2010) 1283-1287


Periodic multilayers of wide photonic bandgap and high reflectance in the visible and near infrared regions are fabricated. Optical properties show that reflectance intensities close to 90% are reached for stacks of only six layers, as well as gap-to-midgap ratios of 50%. The optical response of the hybrid ensemble can be accurately tuned through the number of infiltration cycles performed.

Junio, 2010 | DOI: 10.1002/smll.200902190

In Situ Characterization of the Dynamic Gold-Support Interaction over Ceria Modified Eu3+. Influence of the Oxygen Vacancies on the CO Oxidation Reaction

Hernandez, WY; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Journal of Physical Chemistry C, 114 (2010) 10857-10865


Gold-supported ceria and europium-doped ceria catalysts were prepared by the deposition-precipitation method. The influence of the pretreatment atmosphere and temperature on the concentration of oxygen vacancies and gold dispersion on the Au/CeEti(10) catalyst under actual reaction conditions was investigated by "in situ" X-ray diffraction and Raman analysis. By Raman spectroscopy, a preferential interaction of the gold with the support across the oxygen vacancies was established and correlated with the gold dispersion. The increase in the concentration of oxygen vacancies in the presence of hydrogen induces changes in the gold crystallite size by breaking-off and migration of gold nanoparticles toward the oxygen vacancies on the CeEu(10) support. The activity of the Au/CeEu(10) solid in the CO oxidation reaction was significantly improved when the catalyst was preactivated in a reducing atmosphere. This trend could be associated with the redispersion of gold together with the increase in the concentration of oxygen vacancies in the support.

Junio, 2010 | DOI: 10.1021/jp1013225

Murillo's paintings revealed by spectroscopic techniques and dedicated laboratory-made micro X-ray diffraction

Duran, A; Siguenza, MB; Franquelo, ML; de Haro, MCJ; Justo, A; Perez-Rodriguez, JL
Analytica Chimica Acta, 671 (2010) 1-8


This paper describes one of the first case studies using micro-diffraction laboratory-made systems to analyse painting cross-sections. Pigments, such as lead white, vermilion, red ochre, red lac, lapis lazuli, smalt, lead tin yellow type I, massicot, ivory black, lamp black and malachite, were detected in cross-sections prepared from six Bartolome Esteban Murillo paintings by micro-Raman and micro-XRD combined with complementary techniques (optical microscopy, SEM-EDS, and FT-IR). The use of micro-XRD was necessary due to the poor results obtained with conventional XRD. In some cases, pigment identification was only possible by combining results from the different analytical techniques utilised in this study.

Junio, 2010 | DOI: 10.1016/j.aca.2010.05.004

Environmentally responsive nanoparticle-based luminescent optical resonators

Sanchez-Sobrado, O; Calvo, ME; Nunez, N; Ocana, M; Lozano, G; Miguez, H
Nanoscale, 2 (2010) 936-941


In this work, we demonstrate that optical resonators built using all-nanoparticle-based porous building blocks provide a responsive multifunctional matrix, totally different emission spectra being attained from the same embedded luminescent nanophosphors under varying environmental conditions. We show a clear correlation between modifications in the ambient surroundings, the induced changes of the resonant modes, and the resulting variations in the emission response. The method is versatile and allows nanophosphors of arbitrary shape to be integrated in the cavity. By precise control of the spectral features of the optical resonances, luminescence is strongly modulated in selected and tuneable wavelength ranges. Applications in the fields of sensing and detection are foreseen for these materials.

Junio, 2010 | DOI: 10.1039/b9nr00338j

Self-assembly of supramolecular lipid nanoparticles in the formation of plant biopolyester cutin

Dominguez, E; Heredia-Guerrero, JA; Benitez, JJ; Heredia, A
Molecular Biosystems, 6 (2010) 948-950


The implication of a self-assembly process in the early stages of cutin biosynthesis has been shown by means of antibodies raised against polyhydroxy fatty acid nanoparticles (cutinsomes).

Junio, 2010 | DOI: 10.1039/b927186d

Computational fluid dynamics study of heat transfer in a microchannel reactor for low-temperature Fischer-Tropsch synthesis

Arzamendi, G; Dieguez, PM; Montes, M; Odriozola, JA; Sousa-Aguiar, EF; Gandia, LM
Chemical Engineering Journal, 160 (2010) 915-922


A three-dimensional computational fluid dynamics (CFD) study of heat transfer in a microchannel reactor for the low-temperature Fischer-Tropsch synthesis (FTS) is presented. The microreactor studied is a steel block with 80 square microchannels of 1 mm of side arranged in cross-flow configuration for the transport of syngas and cooling water. Syngas space velocities in the 5000-30,000 h(-1) (SIP) range have been considered. The microreactor exhibited good isothermicity under most simulated conditions. The FTS can be conducted with very low-temperature change between 483 and 523 K within a wide range of CO conversions using boiling water as coolant. To this end the pressure has to be set at the appropriate value between about Sand 35 atm. The pressure would have to be reduced as the CO conversion increases which might have a negative effect on the FTS selectivity to middle distillates. However, adjusting the cooling water flow rate in the range 0.25-250 g min(-1) allows maintaining the FTS temperature at suitable values while avoiding the use of low pressures. Relatively high values of the overall heat transfer coefficient in the 20-320 W m(-2) K-1 range have been obtained. A significant effect of the buoyancy forces on the thermal performance of the microreactor has been found.

Junio, 2010 | DOI: 10.1016/j.cej.2009.12.028

Angular dependence of the intensity of light beams diffracted by colloidal crystals

Lozano, G; Mazzaferri, JE; Dorado, LA; Ledesma, S; Depine, RA; Miguez, H
Journal of the Optical Society of America B-Optical Physics, 27 (2010) 1394-1399


An experimental and theoretical analysis of the angular dependence of the diffracted light beams emerging from three-dimensional colloidal photonic crystals is herein presented. Diffracted beams are identified according to their associated reciprocal-lattice vectors, and their intensities are obtained as a function of the zenithal and azimuthal incidence angles. Significant changes in the beam intensities are observed for large zenithal incidence angles as the azimuthal angle is varied. This phenomenon is related to the excitation of new resonant modes inside the photonic crystal which cannot be observed under normal incidence conditions.

Junio, 2010 | DOI: 10.1364/JOSAB.27.001394

Nonisothermal calorimetric study of the precipitation processes in a Cu-1Co-0.5Ti alloy

Donoso, E; Zuniga, A; Dianez, MJ; Criado, JM
Journal of Thermal Analysis and Calorimetry, 100 (2010) 975-980


The precipitation processes in a Cu-1.0 at.%Co-0.5 at.%Ti (Cu-1.5 at.%Co2Ti) alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900 K shows the presence of two exothermic reactions attributed to the formation of CoTi and Co2Ti particles in the copper matrix. On the basis of enthalpy calculations, it was found that the decomposition begins with the precipitation of CoTi, followed by the formation of Co2Ti particles. The activation energies calculated using the modified Kissinger method were lower than the ones corresponding to diffusion of cobalt and titanium in copper. Kinetic parameters were obtained by a convolution method based on the Johnson-Mehl-Avrami (JMA) formalism. The values obtained for the parameter n were indicative of a particle nucleation process from preexistent nuclei. Microhardness measurements and TEM micrographs confirmed the formation of the mentioned phases.

Junio, 2010 | DOI: 10.1007/s10973-009-0642-y

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


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

Microstructural characterization of ceramic-intermetallic composites using TEM related techniques

Sayagues, MJ; Aviles, MA; Cordoba, JM; Alcala, MD; Gotor, FJ
Journal of the European Ceramic Society, 30 (2010) 1765-1774


TiCxVy/Ni and TiCxNy/Ti-Co composites formed by ceramic and intermetallic binder phases were produced by pressureless sintering at 1400 degrees C from powders synthesized by a mechanically induced self-sustaining reaction (MSR) process. Four different composites were characterized using high-resolution electron microscopic techniques, in both scanning (SEM, HRSEM) and transmission (TEM, HRTEM, ED, EDS and EELS) modes and using an energy filtered technique (EFTEM) associated with electron energy loss spectroscopy (EELS). The microcharacterization showed that the ceramic phase with an fcc-cubic structure displayed a short-range order in many crystals detected by diffuse scattering in the ED patterns. This was possibly due to a sequence of C, N, and vacancies of both atoms along certain directions in the structure. On the other hand, even though the binder phase was introduced as metal in the reaction process, it was formed by Ni-Ti or Co-Ti known intermetallic compounds (NiTi2, Ni3Ti, and Co3Ti). An unknown Ni-Ti intermetallic structure with a Ni:Ti ratio close to 2:1 was only found in one of the synthesized composites and displayed a cubic structure with a lattice parameter, a, of about 8.7 angstrom.

Junio, 2010 | DOI: 10.1016/j.jeurceramsoc.2010.01.039

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


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

The Effect of Water on Particle Size, Porosity and the Rate of Drug Release From Implanted Titania Reservoirs

Lopez, T; Ortiz, E; Alexander-Katz, R; Odriozola, JA; Quintana, P; Gonzalez, RD; Lottici, PP; Marino, LG
Journal of Biomedical Materials Research Part-B Applied Biomaterials, 93B (2010) 401-406


The implantation of controlled drug release devices represents a new strategy in the treatment of neurodegenerative disorders Sol-gel titania implants filled with valproic acid, have been used for this purpose to treat induced epilepsy in rats The kinetics of the drug release depend on. (a) porosity, (b) chemical interactions between valproic acid and surface hydroxyl groups of titania, (c) particle size, and (d) particle size agglomerates The concentration of water used in the hydrolysis reaction is an important variable in the degree of porosity, hydroxylation, and structural defects of the nanostructured titanium oxide reservoir The titanium n-butoxide/water ratio was systematically varied during the sol-gel synthesis, while maintaining the amount of valproic acid constant. Characterization studies were performed using DTA-TGA, FTIR, Raman, TEM, SEM, BET, and in vitro release kinetic measurements The particle agglomerate size and porosity were found to depend on the amount of water used in the sol-gel reactio.

Mayo, 2010 | DOI: 10.1002/jbm.b.31595