Publications

A simple approach to fabricate periodic arrays of conical bumps on silicon (Si) substrate is reported. In the process, a single pulse from a 200 fs laser at 387 nm wavelength was applied on a self-assembled monolayer of 700 nm and 390 nm diameter silica spheres on a n-doped Si (1 0 0) wafer. The surface was irradiated at normal incidence by immersing the silicon substrates in a glass container filled with 1, 1, 2 trichlor-trifluorethan liquid precursors. After laser irradiation, at laser fluences in the range from 1 to 40 J/cm(2), a regular array of conical Si bumps was fabricated. The density of the Si bumps can be varied by varying the particle size diameter. The influence of the medium on the near-field interactions for both sizes silica particles layer is investigated. (C) 2013 Elsevier B.V. All rights reserved.

We report results of noncellular tests, revealing the occurrence of photocatalytic interactions between titanium dioxide (TiO2, titania) nanoparticles and the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromide] cytotoxicity indicator. These interactions induce the reduction of MTT and formation of purple formazan under biologically relevant conditions. Classical MU assays have been performed to evaluate the production of formazan in DMEM-F12 and RPMI-1640 cell culture media (containing 10% fetal bovine serum-FBS) treated with Degussa-P25 TiO2 nanoparticles, in the absence of cells. The colorimetric determinations revealed the noncellular MU to formazan transformation induced by TiO2 nanoparticles, under conditions commonly used for in vitro cytotoxicity testing of nanomaterials. The formazan precipitation was found to be proportional to the TiO2 concentration, being enhanced under laboratory daylight exposure. The photocatalytic nature of the studied effect was assessed under UV irradiation at 365 nm. The biological significance of the reported reaction was established with respect to cellular reference experiments performed on V79-4, HeLa and B16 cell lines. The results show false viability increases with up to 14% (for TiO2 concentrations generally higher than 50 mu g/ml), induced by the TiO2-MTT reaction. This type of artifacts may lead to underestimated toxicity or false proliferation results. (C) 2013 Elsevier Ltd. All rights reserved.

Homojunction transparent thin-film In2O3 transistors were fabricated at room temperature. Self-assembled In2O3 source-channel-drain structures were grown by pulsed electron beam deposition using a shadow mask with a 300 mu m diameter wire as an obstacle placed at similar to 100 mu m distance from the substrate for growing the channel region behind it. The film resistivity varies from similar to 7 x 10(8) Omega cm in the channel region to similar to 10(-3) Omega cm in the source-drain regions. We explain this fact by the relative depletion of the indium incorporated in the channel region of the film due to the reduced flux of ablated species arriving on the substrate behind the obstacle, leading to a relative enrichment in oxygen compared to the source and drain regions. The gate insulator is a Y2O3 film grown by RF magnetron sputtering. The transistor operates in enhanced mode. The subthreshold swing is similar to 0.26 V/decade with an on/off current ratio of 1.5 x 10(7), and the saturation channel mobility is greater than 45 cm(2) V-1 s(-1).

High aspect ratio nanowires of Ni-Cu alloys have been synthesized by potentiostatic electrochemical deposition in etched ion-track membranes. The nickel-to-copper ratio in the nanowires was controlled via the deposition potential and electrochemical bath composition. We present a detailed study of nanowire properties including morphology, composition, and magnetic behavior. We report the magnetic configurations measured as function of the nanowire composition and discuss domain formation, anisotropy aspects, and local easy axis distributions.

The material requirements for structural and armor applications in the future nuclear fusion reactors impose a very high barrier to be surmounted in order to fulfill the safety requirements and reliable operation of the systems. The efforts of NRG and ECN in the developing of materials by Powder / Metal Injection Molding (PIM / MIM) are very promising and show a big potential of this technique as a prospective net shape parts manufacturing method, easily scalable to industrial level. Several M1M materials were developed by the ECN and characterized at NRG within European Fusion Development Agreement (EFDA) Work Programme. Of them, two materials pure tungsten (W) and tungsten doped with 1vol% Y2O3 are demonstrating good potential for likely future use. Therefore, further characterization efforts are needed. The MIM W-1%Y2O3 material seems to be very promising material for armor applications. Extensive thermal shock testing performed at JUDITH 1 up to 1000 cycles and up to 1273 K did not cause crack formation. Additionally, two-component mock-ups were produced using M1M technology. From the very first microstructural investigation of the join area appears that M1M technology can be used as a reliable component joining method.

The formation of an interface between Bi2O3, Fe2O3, BiFeO3, Bi0.5Na0.5TiO3, and the high work function metallic RuO2 is studied using photoelectron spectroscopy with in situ RuO2 deposition. Schottky barrier heights are derived and the valence band maximum energies of the studied materials are aligned with respect to each other as well as to other functional oxides like SrTiO3 and PbTiO3. The energy band alignment follows systematic trends compared to a large number of oxides, and can be understood in terms of the contribution of Fe 3d and Bi 6s/6p (lone pair) orbitals to electronic states near the valence band maximum. The results indicate that the valence band maxima are largely determined by the local environment of the cations, which allows to estimate valence band maximum energies of oxides with multiple cations from those of their parent binary compounds. The high valence band maximum of BiFeO3 is consistent with reported p-type conduction of acceptor doped material, while the high conduction band minimum makes n-type conduction unlikely.

New nanometric systems were produced by using specific parameters of the laser pyrolysis process. Relevant results related to the magnetic behavior of the samples were obtained via SQUID magnetometry and Mossbauer spectroscopy, the data being corroborated with those previously obtained from X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The formed nanocomposites contain iron carbides, iron oxides and metallic iron nanoparticles which relative content and average size depend strongly on experimental specific parameters of the pyrolysis process. The magnetic properties and the local interaction mechanisms were explained by adequate magnetic relaxation and static models. (C) 2013 Elsevier B.V. All rights reserved.

We report new photoluminescence (PL) data generated by pulsed optical excitation on the composites achieved by a mechanico-chemical reaction between ZnS in the cubic (c) and wurtzite (w) phases and polyaniline-emeraldine base (PANI-EB). Under continuous and pulsed optical excitation, powders of the (w)ZnS and (w)ZnS/PANI-EB composites display PL with different spectral compositions. Contrary to expectations, the (c)ZnS and the (c)ZnS/PANI-EB composite displayed weak PL and decay time in the range of nanoseconds. This results from the great involvement of the surface states in nanometric powders which creates efficient channels for the non-radiative recombination of the carriers. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The synthesis of IrQ(ppy)(2)-5Cl has the advantage of a dual phosphorescence (green and red) which comes from the two ligands, phenylpyridine and quinoline. Their spectroscopic properties evidences the absorption range between 350 nm to 700 nm which is composed from the singlet and triplet states, as a result of hybridizations between Ir and the two ligands, the first one being at 625 nm. The first low energy state comes from the quinoline ligand and is responsible for the red phosphorescence at 660 nm, as results from the Density Functional Theory (DFT) analysis. The hybridization between Ir 5d orbitals and pi ligand orbitals shows strong metallic character with phenylpyridine orbitals (66% and 43%) and weak metallic character with quinoline ligand (16.8%). This fact suggests weak phosphorescence intensity in the emission spectra. Population analysis of each metallic orbital shows a small charge delocalization on the quinoline ligand for the first molecular orbital and a strong delocalization on the phenylpyridine ligands. Solvation effects induce a tuning process for the phosphorescence by changing of the matrix of the organometallic compounds which can be adjusted by the strength of intermolecular dipole-dipole interactions, using a doped guest-host molecular organic thin film system.