National Institute Of Materials Physics - Romania

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5714 articles found

2241. Optics of microlenses created by irradiation of As2S3 amorphous chalcogenide films with femtosecond laser pulses

Authors: Popescu, M; Velea, A; Miclos, S; Savastru, D

Published: APR 1 2013, PHILOSOPHICAL MAGAZINE LETTERS, 93, 220, DOI: 10.1080/09500839.2012.760058

Arrays of microlenses have been created on the surface of thin amorphous films of As2S3 by localized photoexpansion induced by femtosecond laser pulses. The profile of a typical microlens has been mathematically described. Ray-tracing analysis has been performed to determine the focal points in the red and near-infrared spectrum of electromagnetic radiation. These lie at distances of 1.21m at =650nm and 1.33m at =1.5m above the top of the microlens. It is suggested that the microlenses could be used in two-dimensional optoelectronic circuits or in fibre optics.

2242. Structural properties of silver doped hydroxyapatite and their biocompatibility

Authors: Ciobanu, CS; Iconaru, SL; Pasuk, I; Vasile, BS; Lupu, AR; Hermenean, A; Dinischiotu, A; Predoi, D

Published: APR 1 2013, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 33, 1402, DOI: 10.1016/j.msec.2012.12.042

The aim of this study was to obtain a novel hydroxyapatite-based material with high biocompatibility. The structural properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The X-ray diffraction studies revealed the characteristic peaks of hydroxyapatite in each sample. Other phases or impurities were not observed. The scanning electron microscopy observations suggest that the doping components have no influence on the surface morphology of the samples, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O) and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) and X-ray Photoelectron Spectroscopy analyses. Nanocrystalline silver doped HAp stimulated viability and potentiated the activation of murine macrophages. (C) 2012 Elsevier B.V. All rights reserved.

2243. ZnO films and nanorod/shell arrays electrodeposited on PET-ITO electrodes

Authors: Sima, M; Vasile, E; Sima, M

Published: APR 2013, MATERIALS RESEARCH BULLETIN, 48, 1586, DOI: 10.1016/j.materresbull.2012.12.045

In this work, ZnO films, nanorod and nanorod/shell arrays were synthesized on the surface of PET-ITO electrodes by electrochemical methods. ZnO films with high optical transmittance were prepared from a zinc nitrate solution using a pulsed current technique with a reduced pulse time (3 s). The X-ray diffraction pattern of ZnO film deposited on PET-ITO electrode showed that it has a polycrystalline structure with preferred orientations in the directions [0 0 2] and [1 03]. ZnO nanorods were synthesized on electrochemical seeded substrate in an aqueous solution containing zinc nitrate and hexamethylenetetramine. In order to increase the stability of PET-ITO electrode to electrochemical and chemical stresses during ZnO nanorods deposition the surface of the electrode was treated with a 17 wt% NH4F aqueous solution. Electrochemical stability of PET-ITO electrode was evaluated in a solution containing nitrate ions and hexamethylenetetramine. ZnO nanorod/shell arrays were fabricated using eosin Y as nanostructuring agent. Photoluminescence spectra of ZnO nanorod and ZnO nanorod/shell arrays prepared on the surface of PET-ITO electrode were discussed comparatively. By employing the 1.5 mu m-length ZnO nanorod/shell array covered with a Cu2O film a photovoltaic device was fabricated on the PET-ITO substrate. (C) 2012 Elsevier Ltd. All rights reserved.

2244. Dependence of the strain diffraction line broadening on (hkl) and sample direction in textured polycrystals

Authors: Popa, NC; Lungu, GA

Published: APR 2013, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 46, DOI: 10.1107/S0021889812051928

A new phenomenological approach describing the dependence of the strain diffraction line breadth on direction in both crystal and sample is presented. For a negligibly small dependence on the direction in the sample, these models reduce to those for anisotropic strain broadening that already exist in the literature and which are implemented in popular Rietveld codes. The new model is appropriate for implementation in the Rietveld programs able to process simultaneously diffraction patterns recorded in multiple directions in a sample.

2245. Microstructure and electrical properties of zirconia and composite nanostructured ceramics sintered by different methods

Authors: Vasile, BS; Andronescu, E; Ghitulica, C; Vasile, OR; Curechiu, L; Scurtu, R; Vasile, E; Trusca, R; Pall, L; Aldica, V

Published: APR 2013, CERAMICS INTERNATIONAL, 39, 2543, DOI: 10.1016/j.ceramint.2012.09.013

The aim of this study is the preparation and characterization of dense cubic zirconia ceramics and zirconia nanocomposites (reinforced with 5 wt% alumina). The powders were obtained through sol-gel methods and densified using classical sintering and spark plasma sintering (SPS) methods. The obtained ceramics were characterized through X-ray diffraction, scanning electron microscopy and impedance spectroscopy at room and high temperature. The average grain size of cubic zirconia particles was found to be approximately 8 and 2.5 mu m for the classical sintering and 99 nm for SPS. The alumina particles in composites have an average grain size of 0.7 mu m for classical sintering and 53 nm for SPS ones. The total conductivity for nanocomposites sintered through both methods was also determined. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

2246. Inhibition of the detrimental double vortex-kink formation in thick YBa2Cu3O7 films with BaZrO3 nanorods

Authors: Miu, D; Ivan, I; Crisan, A; Mele, P; Jakob, G; Miu, L

Published: APR 2013, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 26, DOI: 10.1088/0953-2048/26/4/045008

We investigated the temperature (T) variation of the normalized magnetization relaxation rate S and of the corresponding normalized vortex-creep activation energy U* = T/S for YBa2Cu3O7 films containing BaZrO3 nanorods, with the external magnetic field H oriented perpendicular to the film surface. It was found that by increasing the film thickness and using nanodot decorated substrates the high-T S(T) maximum appearing at low H is substituted by a minimum in S(T). As revealed by the analysis of the current density dependence of U*, this behaviour is due to the inhibition of vortex excitations involving double vortex-kinks and superkinks formation in the investigated thick films, owing to the large nanorod splay and pinning energy dispersion.

2247. Prediction of half metallic properties in Ti2CoSi Heusler alloy based on density functional theory

Authors: Birsan, A; Palade, P; Kuncser, V

Published: APR 2013, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 331, 112, DOI: 10.1016/j.jmmm.2012.11.029

The electronic and magnetic properties of Ti2CoSi Heusler compound are investigated using density functional calculations. The optimized lattice constant is found to be 6.030 angstrom. The compound is a half-metallic ferromagnet with an energy gap in minority spin channel of 0.652 eV at equilibrium lattice constant, which leads to a 100% spin-polarization. The obtained total magnetic moment from spin-polarized calculations is 3.0 mu(B)for values of lattice constants higher than 5.941 angstrom. The half-metallicity is spoiled for a compressed volume of 4%, suggesting a possible application as pressure sensitive material. (C) 2012 Elsevier B.V All rights reserved.

2248. Laser induced breakdown spectroscopy surface analysis correlated with the process of nanoparticle production by laser ablation in liquids

Authors: Apostol, I; Damian, V; Damian, R; Nistor, LC; Pascu, A; Staicu, A; Udrea, C

Published: APR 2013, HYPERFINE INTERACTIONS, 216, 143, DOI: 10.1007/s10751-012-0739-8

Laser induced ablation of solids situated in liquids (LAL) was used in order to produce nanoparticles. Laser induced breakdown spectroscopy (LIBS) surface analysis correlated with the process of nanoparticle production by LAL was applied to explain the composition of the obtained nanoparticles as determined by Electron Dispersive X-ray Spectroscopy (EDS). In the case of aluminum rods placed in distilled water irradiated with pulsed laser radiation (355 nm wavelength, 6 ns pulse length) we have obtained spheric nanoparticles with dimensions lower than 100 nm. Quantitative EDS analyses on the obtained spheres showed the presence of, Al, O, and Si. This indicates that probably the composition of the nanoparticles is an aluminum silicate. LIBS analysis on the aluminum target have shown the presence of a Si line with low intensity indicating a small quantity of silicon in the first ablated layers. The LIBS spectra for a sequence of pulses evidenced also that the intensity of the aluminum lines after a number of pulses decreases. This means that the quantity of ablated material becomes smaller due to the ablation depth decrease.

2249. Some comments on Eu-151 Mossbauer spectroscopy

Authors: Bibicu, I

Published: APR 2013, EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS, 62, DOI: 10.1051/epjap/2013120328

The possibility to do surface measurements on sample containing Eu-151 by detection of Auger electrons delivered in the decay process of the Mossbauer nucleus is briefly presented herein. The test measurements have been carried out on Eu2O3 powder sample. A higher resonance effect and a lower line width have been obtained in backscattering geometry compared with transmission geometry.

2250. Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion

Authors: Ganea, CP

Published: APR 2013, CENTRAL EUROPEAN JOURNAL OF PHYSICS, 11, 511, DOI: 10.2478/s11534-013-0204-6

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.