National Institute Of Materials Physics - Romania

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5781 articles found

3901. Nanostructural configurations in As2S3 glass

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

Published: APR 2006, PHYSICS AND CHEMISTRY OF GLASSES-EUROPEAN JOURNAL OF GLASS SCIENCE AND TECHNOLOGY PART B, 47, 157, DOI:

Various closed nanocluster configurations based on the stoichiometric arsenic-chalcogen composition have been built and relaxed by a computer Monte Carlo procedure. They can be used in the construction of the glass network. A model with random packing of various large, closed nano-clusters has been devised and fairly good agreement with experimental data for As2S3 has been obtained.

3902. Model of the interband nonlinear absorption in amorphous chalcogenides: Quasi-linear analytical solutions

Authors: Babin, V; Popescu, M; Ciobanu, M; Nicolae, ND; Talianu, C; Ciuciu, G

Published: APR 2006, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 17, 314, DOI: 10.1007/s10854-006-6949-6

It is proposed a quasi-linear algorithm for the solving the kinetic equations system, which describes the excitation and relaxation processes in the electronic and phononic subsystems of amorphous chalcogenides. The nonlinear interaction between an optical field and an amorphous chalcogenide medium is analyzed. The nonlinear interaction between an excitation incident optical field and the non-crystalline chalcogenide materials, evidences the specific nonlinear phenomena in amorphous semiconductors, which have no correspondent in the case of crystalline semiconductors. The model is limited to phenomena occurring in chalcogenide semiconductors, simultaneously with the optical field propagation, by neglecting the excitation phenomena.

3903. The 'in-plane' angular spin distribution in layered systems as obtained by Fe-57 Mossbauer spectroscopy (vol 196, pg 135, 2002)

Authors: Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR

Published: APR 2006, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 245, 542, DOI: 10.1016/j.nimb.2006.01.022

3904. Influence of Ca2+ and Mg2+ as twinned ions on zirconia powder stability

Authors: Volceanov, E; Volceanov, A; Stoleriu, S; Plapcianu, C

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 592, DOI:

Microstructure and the sintering behaviour of zirconia with twinned stabiliser ions: Ca2+ + Mg-2 in oxidative and in inert environment respectively obtained by solid state reactions method were studied. The specimens were cured at 1550 degrees C and 1750 degrees C in air in a kiln with methane gas. Samples with the same composition were sintered at 1550 degrees C in Argon in electrical furnace with (graphite electrodes). Their sinterability, microstructure as well as stability was studied The properties were compared as function of the processing route, the compositions stabilised in argon protective environment at 1550 degrees C or in air at 1750 degrees C, a totally stabilisation process was effective.

3905. Spin configurations in exchange coupled magnetic phases studied by Mossbauer spectroscopy

Authors: Kuncser, V; Keune, W; Stromberg, F; Schinteie, G; Filoti, G

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 517, DOI:

The ability of the Fe-57 Mossbauer technique to reveal the spin structures in exchange coupled magnetic phases containing iron is emphasized. Experimental results obtained on layered exchange-bias systems are presented. The influence of the ferromagnetic top layer on the out-of-plane spin component of the pinning antiferromagnetic-like layer, in both Fe/FeSn2 and Fe/Fe-Gd-B exchange bias systems, is discussed.

3906. The magnetic effects in Sr2FeMoO6 perovskite type compound obtained by soft chemistry

Authors: Aldica, G; Plapcianu, C; Badica, P; Valsangiacom, C; Popescu, B

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 463, DOI:

Recently, a double perovskite oxide, Sr2FeMoO6, has been reported to show a very sharp magnetoresistance (MR) response at relatively small-applied fields and at high temperatures. The half-metallic state of this compound ensures a theoretical magnetic moment of 4 mu(B) per formula unit. Ordering control is expected to be influenced by the synthesis route. In this regard, in this article, perovskite samples were obtained from the liquid phase, using oxalic acid as complexing agent. Application of a field above 0.08 T increases the zero-field-cooled (ZFC) magnetization. Below this field, for the ZFC-curves measured from 2 K up to 400 K, magnetization increases, reaching a peak at T-cups(ZFC), before decreasing cups gradually to a paramagnetic state. Saturation moment is relatively low (2.1-2.2 mu(B)), probably due to anti-site defects, as suggested in the literature.

3907. Fabrication and characterisation of GaAs Gunn diode chips for applications at 77 GHz in automotive industry

Authors: Forster, A; Stock, J; Montanari, S; Lepsa, MI; Luth, H

Published: APR 2006, SENSORS, 6, 360, DOI:

GaAs-based Gunn diodes with graded AlGaAs hot electron injector heterostructures have been developed under the special needs in automotive applications. The fabrication of the Gunn diode chips was based on total substrate removal and processing of integrated Au heat sinks. Especially, the thermal and RF behavior of the diodes have been analyzed by DC, impedance and S-parameter measurements. The electrical investigations have revealed the functionality of the hot electron injector. An optimized layer structure could fulfill the requirements in adaptive cruise control (ACC) systems at 77 GHz with typical output power between 50 and 90 mW.

3908. Manganese doped sol-gel materials with catalytic properties

Authors: Crisan, M; Raileanu, M; Preda, S; Zaharescu, M; Valean, AM; Popovici, EJ; Teodorescu, VS; Matejec, V; Mrazek, J

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 819, DOI:

In the present study manganese doped alumina and silica gels and thin films deposited on different substrates (refractory metals, silicon wafers) were obtained by the alkoxide and aqueous routes of the sol-gel method. The characterization of the films was realized by X-ray diffraction (XRD), and spectroellipsometry (SE) methods. The un-supported gels (obtained by the gelation of the solutions used for the film deposition) were characterized by DTA/TG analysis, IR spectroscopy, transmission electron-microscopy and electron diffraction (TEM and SAED) and BET method (adsorption of krypton at temperature of liquid nitrogen) for surface area and pores volume determination. The sol-gel materials were tested as catalysts for the ozone decomposition.

3909. Positron annihilation lifetime spectroscopy as experimental probe of free volume concepts in network glasses

Authors: Shpotyuk, O; Kovalskiy, A; Filipecki, J; Kavetskyy, T; Popescu, M

Published: APR 2006, PHYSICS AND CHEMISTRY OF GLASSES-EUROPEAN JOURNAL OF GLASS SCIENCE AND TECHNOLOGY PART B, 47, 135, DOI:

Positron annihilation lifetime spectroscopy (PALS) is tested for use as an alternative experimental probe of free volume concepts in network chalcogenide glasses. PALS measurements are carried out within binary As-Se and ternary GeAs(Sb)-S systems on the examples of g-As2Se3 and samples from stoichiometric As(Sb)(2)S-3-GeS2 and nonstoichiometric As(Sb)(2)S-3-Ge2S3 cross sections. The effect of high energy gamma-irradiation on PALS parameters is studied for ternary glass compositions. The role of induced defect related positron traps in annihilation processes is illustrated. The correlations between nanovoid sizes obtained from PALS, Monte Carlo simulation and first sharp diffraction peak (FSDP) measurements in the framework of Elliott's model are established on the example of g-As2Se3, in order to study the nanovoid topology in the real glass structure. It is shown that nanovoids with average radius of 2.9 angstrom, being effective traps for positrons with 0.37 ns defect related lifetime, are also detected within nanovoid distribution data obtained from Monte Carlo simulation. Suggesting that this group of nanovoids is responsible for the void based origin of FSDP, the analytical relationship between FSDP position and nanovoid diameter is proposed for layer like As2X3-type structures.

3910. New polypyrrole-multiwall carbon nanotubes hybrid materials

Authors: Turcu, R; Darabont, AL; Nan, A; Aldea, N; Macovei, D; Bica, D; Vekas, L; Pana, O; Soran, ML; Koos, AA; Biro, LP

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 647, DOI:

We report the synthesis and characterization of new hybrid materials based on conducting polypyrrole (PPY) and multi wall carbon nanotubes (MWCNTs). MWCNTs were prepared by spray-pyrolysis of liquid hydrocarbon-ferrocene solution in an Ar atmosphere. The composites (PPY-CNT) were obtained by in-situ chemical oxidative polymerization of pyrrole in aqueous solution containing MWCNTs. The addition of a water based Fe3O4 nanofluid to the polymerization solution results in the formation of a new hybrid nanostructure of MWCNTs coated with PPY containing magnetic nanoparticles. The properties of PPY composites were investigated by TEM, SEM, FTIR spectroscopy and X-ray diffraction (XRD) measurements. MWCNTs covered with PPY have a rough surface, containing some globular forms typical for the polymer. Significant differences between IR spectra for PPY and PPY-CNT nanocomposites appear for the bands ascribed to pyrrole ring vibrations, suggesting that an interaction between the polymer and CNT occurs and this could change the polymer conformation. XRD analysis shows that the crystalline structure of MWCNTs doesn't change significantly by the association with conducting PPY.