Time filter

Source Type

Sauthier G.,Catalan Institute of Nanoscience and Nanotechnology | Figueras A.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,National Institute for Lasers
Journal of the American Ceramic Society | Year: 2012

Hemispherical and columnar TiO 2 array were produced by reactive pulsed laser deposition (PLD) using self-assembled polystyrene (PS) monolayers as templates. The integration of PS microspheres self-assembly processes and PLD permits the creation of periodic arrays in hexagonal arrangement. The micro/nano array architecture demonstrates outstanding catalytic performance in the degradation of methylene blue dye in aqueous solution. The obtained results suggest that besides other structural characteristics the large specific surface area plays an essential role in the improvement of photoactivity of oxide semiconductor catalyst. © 2012 The American Ceramic Society.

Sauthier G.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,National Institute for Lasers | Figueras A.,Catalan Institute of Nanoscience and Nanotechnology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

Nitrogen-doped TiO 2 vertically aligned columnar arrays were grown by reactive pulsed laser deposition using self-assembled polystyrene (PS) microsphere monolayers as templates and TiO 2 hemispherical arrays as buffers. The created columnar arrays showed significantly enhanced photocatalytic activity as compared with the reference thin films grown under identical experimental conditions but in the absence of the PS templates, both under visible- as well as UV-light irradiation. The photocatalytic activity decreased with the increase in the nitrogen doping level, suggesting the existence of a threshold value for the nitrogen incorporation in the TiO 2 crystal lattice. © 2012 American Chemical Society.

Sauthier G.,Catalan Institute of Nanoscience and Nanotechnology | Perez Del Pino A.,CSIC - Institute of Materials Science | Figueras A.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,Catalan Institute of Nanoscience and Nanotechnology | Gyorgy E.,National Institute for Lasers
Journal of the American Ceramic Society | Year: 2011

Ag nanoparticles and Ag-TiO2 nanostructures were grown on (001) SiO2 quartz substrates by pulsed laser deposition using a KrF* excimer laser source (λ = 248 nm, τFWHM∼10 ns, I = 10 Hz) for the irradiation of Ag and TiO2 targets. The obtained structures were characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-visible absorption spectroscopy. Photocatalytic activity was evaluated under near-UV light illumination by decomposition of methylene blue. The relationship between the laser synthesis process parameters and nanoparticles' chemical composition, crystal structure, morphology, shape and size distribution on the substrate surface were investigated and correlated with their optical properties. The established experimental parameters were used for the synthesis of nanostructures consisting of anatase phase TiO2 thin films covered by Ag nanoparticles for photocatalytic applications. The optimum experimental conditions were determined which ensure significantly improved photoactivity in the presence of Ag nanoparticles as compared to the bare oxide surface. © 2011 The American Ceramic Society.

Baldea I.,University of Heidelberg | Baldea I.,National Institute for Lasers | Koppel H.,University of Heidelberg | Wenzel W.,Karlsruhe Institute of Technology
Physical Chemistry Chemical Physics | Year: 2013

We report results of quantum chemical calculations for the neutral and anionic species of (4,4′)-bipyridine (44BPY), a prototypical molecule with a floppy degree of freedom, placed in vacuo and in solvents. In addition to equilibrium geometries and vibrational frequencies and spectra, we present adiabatic energy curves for the vibrational modes with significant intramolecular reorganization upon charge transfer. Special attention is paid to the floppy strongly anharmonic degree of freedom of 44BPY, which is related to the most salient structural feature, namely the twist angle θ between the two pyridine rings. The relevance of the present results for molecular transport will be emphasized. We show that the solvent acts as a selective gate electrode and propose a scissor operator to account for solvent effects on molecular transport. Our result on the conductance G vs. cos2θ is consistent with a significant transmission in perpendicular conformation indicated by previous microscopic analysis. © 2013 The Owner Societies.

Baldea I.,University of Heidelberg | Baldea I.,National Institute for Lasers
Chemical Physics | Year: 2012

The influence of the stochastic fluctuations at contacts on the electron transport through molecular junctions based on alkanedithiols is investigated theoretically. Results are presented, which demonstrate that the transition voltage V t is insensitive to fluctuations in the electrode-molecule hopping integrals. By contrast, reasonably large fluctuations (δJ∼2eV) in the Coulomb contact interaction J, included via an extended Newns-Anderson model, lead to fluctuations in the molecular orbital energetic alignment 0, which are consistent with the fluctuations in V t observed experimentally. The impact of these J- (or 0-) fluctuations on the conductance G is considerably stronger than on V t. The G-fluctuations driven by δJ represent a substantial fraction of the fluctuations displayed by experimental conductance histograms. The electron system for J≠0 is correlated, i.e., it cannot be described within a single-particle (Landauer-based) picture. However, in the J-range of interest, the ratio Vt/ 0 turns out to be only weakly dependent on J. The weak impact of J on the ratio Vt/ 0 is important because it suggests that, even in the presence of realistically strong electron correlations, transition voltage spectroscopy can be a useful tool of investigation. © 2012 Elsevier B.V. All rights reserved.

Baldea I.,University of Heidelberg | Baldea I.,National Institute for Lasers
Journal of Physics and Chemistry of Solids | Year: 2012

The initial interpretation of the transition voltage (V t) spectroscopy within a tunneling barrier picture has been later challenged within calculations based on the Simmons model. In this communication, it will be shown that the predictions of the Simmons model for V t represent artefacts of an inadequate WKB-type constant barrier approximation, which are exacerbated by those calculations by an incorrect expression of the image potential. © 2012 Elsevier Ltd. All rights reserved.

Clatot J.,CNRS Laboratory of Chemistry and Reactivity of Solids | Campet G.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | Zeinert A.,CNRS Condensed Matter Physics Laboratory | Labrugere C.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | And 2 more authors.
Solar Energy Materials and Solar Cells | Year: 2011

Si doped zinc oxide (SZO, Si 3%) thin films are grown at low substrate temperature (T≤150 °C) under oxygen atmosphere, using pulsed laser deposition (PLD). Si addition leads to film amorphization and higher densification. Hall effect measurements indicate a resistivity of 7.9×10-4 Ω cm for SZO thin films deposited at 100 °C under optimized 1.0 Pa oxygen pressure. This value is in good agreement with optical resistivity simulated from the transmittance spectra. XPS measurements suggest more than one oxygen environment, and a Si oxidation state lying in between 2 and 3 only. As a matter of fact, the values of both measured and simulated carrier numbers are smaller than the ones expected, assuming that all Si cations in the ZnO matrix are at the 4+ oxidation state. Finally, the differences in the electrical and optical properties of SZO thin films deposited both on glass and PET substrates confirm the strong dependency of the electronic properties to the film crystallinity and stoichiometry in relationship with the substrate nature. © 2011 Elsevier B.V.

Gherendi F.,National Institute for Lasers | Nistor M.,National Institute for Lasers | Mandache N.B.,National Institute for Lasers
IEEE/OSA Journal of Display Technology | Year: 2013

In this work, we report on the fabrication of hybrid n-channel thin film transistors using paper as substrate and gate insulator, and indium oxide In2O3 thin films as channel layer, and contacts for the source, drain and gate respectively. Capacitor paper having 10 μ thickness was used. In2O3 thin films were grown by pulsed electron beam deposition method at room temperature. The gate leakage current was 20 nA at 5 V and the on/off current ratio up to 6× 104, limited mainly by the gate leakage. The transfer characteristics IdVgs-showed a memory effect with a threshold voltage of 0.8 V in '0' state and-3.6 in '1' state. The drain current-voltage characteristics family IdVds-showed saturation currents up to 3.5 mA in '1'state and about 500μA in '0' state. The subthreshold swing was 0.3-0.5 V/decade. © 2013 IEEE.

Nemtanu M.R.,National Institute for Lasers | Brasoveanu M.,National Institute for Lasers
Starch/Staerke | Year: 2016

The current study brings to light new aspects of degradation of polysaccharides by physical methods, namely degradation of amylose exposed in the solid state to the accelerated electron beam, in the presence of oxygen, in the range of 10-50kGy. Effects of irradiation on amylose were investigated by gel-permeation chromatography, Fourier transform infrared spectroscopy, and scanning electron microscopy. In order to evaluate quantitatively, the radiation degradation of amylose, radiochemical yield of degradation, degradation rate constant, and half value dose of molecular weights were determined. The results indicated the main-chain scission of amylose, which led to the reduction of its molecular weight and molecular weight distribution. Changes of amylose spectral features related to the frequency and intensity of some bands indicated an alteration of the structural integrity induced by the electron beam. The scanning electron micrographs revealed the appearance of smaller fragments by amylose structure disruption as a result of irradiation. Consequently, degradation of amylose in the solid state can effectively be controlled by electron beam irradiation. This novel study may be a useful starting point for preparation or processing of amylose-based matrices by using electron beam treatment. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nistor M.,National Institute for Lasers | Gherendi F.,National Institute for Lasers | Mandache N.B.,National Institute for Lasers
Applied Surface Science | Year: 2012

Pulsed energy beam deposition methods like pulsed-laser deposition (PLD) or pulsed-electron beam deposition (PED) allow the formation of smooth, dense and crystalline oxide thin films. The angular distribution of the ablated flux from the target and the thin film thickness profile were extensively studied for PLD for a wide range of materials and growth conditions. In the case of complex oxide compounds, the angular distribution of the various species emitted by the target will determine the precise composition of the films. In this work we report on the determination of the angular distributions of the species emitted from a Ba xSr 1-xTiO 3 (BST) target. A comparison between these results obtained by PED and PLD methods is presented and discussed in the frame of Anisimov's model. A slightly broader shape of the angular distribution for PED than that for PLD is explained taking into account the differences in the spot size and fluence between the pulsed electron beam and laser beam and a small collisional broadening of the angular distribution in the case of PED. The stoichiometry is preserved at all angles. © 2012 Elsevier B.V.

Loading National Institute for Lasers collaborators
Loading National Institute for Lasers collaborators