National Institute Of Materials Physics - Romania

Publications

5781 articles found

3291. Physical properties of CdTe nanowires electrodeposited by a template method, for photovoltaic applications

Authors: Ion, L; Enculescu, I; Antohe, S

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3246, DOI:

Nanowires made of CdTe were produced by using a template method. Polymer ion track foils (30 micrometers thick) were used as templates, after a proper chemical etching. Nanowires were electrochemically grown in the resulting pores. A discussion of the observed correlations between the morphological/structural properties of the wires and the growth conditions is given. Electrical properties of the arrays of nanowires were studied in the temperature range of 40 K - 300 K, after contacting them by sputtering a gold layer on top of the membranes. Symmetric, non-linear I-V characteristics were recorded in the voltage range used and an activated electrical resistance was observed in the ohmic regime.

3292. Surfactant involved in Copper Sulfide Nanocrystallites Synthesis

Authors: Simonescu, CM; Teodorescu, VS; Capatina, C

Published: DEC 2008, REVISTA DE CHIMIE, 59, 1329, DOI:

This paper presents the obtaining of copper sulfide CuS (covelite) from Cu(CH3COO)(2)center dot H2O and thioacetamide (TAA) system. The reaction was conducted in presence or absence of sodium-bis(2-ethylhexyl) sulfosuccinate (Na-AOT). The effects of various reaction parameters on the size and on the shape of nanoparticles have been examined. CuS obtained was characterized by X ray diffraction, IR spectroscopy, TEM - transmission electron microscopy and SAED selected area electron diffraction. The influence of surfactant to the shape and size of CuS (covellite) nanocrystals was established. The size of the nanocrystals varied from 10-60 nm depending on the reaction conditions such as quantity of surfactant.

3293. Direct measurement of depth-dependent Fe spin structure during magnetization reversal in Fe/MnF2 exchange-coupled bilayers

Authors: Macedo, WAA; Sahoo, B; Eisenmenger, J; Martins, MD; Keune, W; Kuncser, V; Rohlsberger, R; Leupold, O; Ruffer, R; Nogues, J; Liu, K; Schlage, K; Schuller, IK

Published: DEC 2008, PHYSICAL REVIEW B, 78, DOI: 10.1103/PhysRevB.78.224401

We measured directly the depth-dependent Fe spin rotation upon magnetization reversal in exchange-coupled Fe/MnF2 bilayers using nuclear resonant scattering of synchrotron radiation from an Fe-57-probe layer buried at different depths within the Fe film. Our results show that the exchange-biased ferromagnetic layer develops a noncollinear spin structure along the film normal direction, reminiscent of a partial domain wall parallel to the Fe/MnF2 interface. This is contrary to most theoretical models of exchange bias which assume a collinear spin structure in the ferromagnetic layer.

3294. Origin of the plateau in the temperature dependence of the normalized magnetization relaxation rate in disordered high-temperature superconductors

Authors: Miu, L; Miu, D; Petrisor, T; El Tahan, A; Jakob, G; Adrian, H

Published: DEC 2008, PHYSICAL REVIEW B, 78, DOI: 10.1103/PhysRevB.78.212508

The temperature T dependence of the normalized magnetization relaxation rate S in optimally doped YBa(2)Cu(3)O(7-delta) films with the external dc magnetic field H oriented along the c axis exhibits the well-known plateau in the intermediate T range, associated with the presence of elastic (collective) vortex creep. The disappearance of the S(T) plateau in the high-H domain (H >= 20 kOe) is not completely understood. We show that in the case of high-temperature superconductors with significant quenched disorder the S(T) plateau is directly related to a crossover in the vortex-creep process generated by the macroscopic currents induced in the sample. In dc magnetization measurements the creep-crossover temperature decreases rapidly with increasing H, reaching the low-T region where the magnetization decay is dominated by micro flux jumps. Consequently, at high H no well-defined elastic-creep domain is present and the S(T) plateau disappears.

3295. The modification induced by UV radiation in spherical microlenses made of glassy arsenic sulphide

Authors: Rusu, M; Velea, A; Popescu, M

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3171, DOI:

Spherical arsenic chalcogenide glass microlenses have been attached to optical fibers. The assembly was subjected to UV-radiation for different time intervals in different conditions of temperature. As a consequence, the focusing of the beam changes due to the modification of the refractive index, and of the structure, induced by photo-melting followed by crystallization. In the same time for high irradiation times the habitus of the lens changes into a prismatic one due probably to photomelting of the glass accompanied by a crystallization process.

3296. Synthesis and characterization of polyethylene/C-60 fullerene structures by photoluminescence

Authors: Rusen, E; Marculescu, B; Preda, N; Mihut, L

Published: DEC 2008, JOURNAL OF POLYMER RESEARCH, 15, 451, DOI: 10.1007/s10965-008-9190-6

Fullerene C-60 has attracted attention due to its special chemical and physical properties. However, its poor solubility and processability arise difficulties in practical applications. These problems may be surpassed by grafting C-60 on polymers. This study presents the synthesis of the polyethylene/maleic anhydride copolymers and C-60 structures and their characterization by photoluminescence. The synthesis of the material is based upon the reaction of fullerene C-60 with amino groups containing in the polymer chains. In the first step, some polyethylene (PE)/maleic anhydride (MA) copolymers having 1, 3, 6 and 10 wt.% anhydride groups were reacted with an amine compound. The following step consists in the reaction of C-60 with the amine groups. A proof that the structures synthesized contain C-60 is given by the photoluminescence spectra.

3297. Alternating barium stearate and copper stearate LB thin films

Authors: Popescu, M; Lorinczi, A; Velea, A; Sava, F

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3415, DOI:

Alternating layers based on copper and barium stearate have been prepared. The interlayer distance for both type of stearates have been determined by X-ray diffraction. It was found that the interlayer distance for an alternating assembly depends on the actual type of the stearate layer. Thus we demonstrated the possibility to control the inter-layer distance by choosing an appropriate sequency of layers. It is suggested that such layers may serve as high precision thickness standard at the angstrom level.

3298. Sintered fused silica based composites

Authors: Volceanov, E; Neagu, R; Volceanov, A; Plapcianu, C; Matovic, B; Niciu, H; Valsangiacom, C

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3228, DOI:

In present work, complex mixtures were designed based on fused SiO2, beta-SiC and different oxide additives. The addition of Al2O3 and mulite - 3Al(2)O(3) 2SiO(2) influence was investigated in order to obtain high temperature strength, thermal shock resistant and corrosion resistant composites. Thermal treatment was conducted in conventionally electric furnace in air and in argon respectively, in the 800-1250 degrees C temperature range. Sintered composites were characterised by bulk density, open porosity, and thermal shock resistance and thermal expansion measurements. The crystalline phase evolution in conjunction with each heat curing procedure was analysed by X-ray diffraction and FTIR spectrometry. Microstructure investigation of sintered samples was carried using scanning and transmission electron microscopy. The relationship between the FTIR spectra and structure of the powders and sintered composites was explained.

3299. Electrochemical growth and characterization of nanostructured ZnO thin films

Authors: Ghica, C; Enculescu, I; Nistor, LC; Matei, E; Van Tendeloo, G

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3240, DOI:

ZnO is a wide band-gap (ca. 3.4 eV) semiconductor, piezoelectric, pyroelectric, biocompatible, transparent in the visible spectrum and UV light emitting material. The fabrication in 2001 of the first nanobelts of semiconductor oxide materials lead to a rapid expansion of researches concerning one dimensional nanostructures (nanotubes, nanowires, nanobelts), given their possible application in optics, optoelectronics, piezoelectricity, catalysis. Researches carried on up to date evidenced the possibility to obtain an extraordinary variety of ZnO nanostructures, in function of the experimental parameters and the used growth methods. In this work we present morphostructural results on nanostructured ZnO layers obtained by electrochemical deposition. The films have been grown on gold covered glass plates and Si wafers, in various experimental conditions such as: nature of the wetting agents, electrical polarization of the substrate (continuous, pulsed). The influence of the growth conditions on the crystalline structure and morphology of the films is revealed by scanning and transmission electron microscopy studies. The films show a variety of growth morphologies, from entangled-wires-like to honeycomb-like layers. These large-specific-surface layers will be tested as nanostructured substrates for photovoltaic cells with improved efficiency.

3300. Pyramidal morphology of InN thin films deposited by reactive RF-magnetron sputtering

Authors: Zoita, NC; Besleaga, C; Braic, L; Mitran, T; Vlaicu, M

Published: DEC 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 797, DOI:

Indium nitride is an attractive semiconductor material for optoelectronic applications, high-speed electronics and solar cells. We report deposition of polycrystalline InN thin films with pyramidal morphology on different substrates by reactive RF magnetron sputtering method. The morphological characterization if the films are presented in corroboration with the deposition parameters and the observed crystallographic structure.