National Institute Of Materials Physics - Romania

Publications

5840 articles found

4581. Quantum macroscopic coherent phenomena in biocommunication

Authors: Branescu, M

Published: 2002, ALT'01 INTERNATIONAL CONFERENCE ON ADVANCED LASER TECHNOLOGIES, 4762, 391, DOI: 10.1117/12.478664

The proposal of coherent electromagnetic processes as the engine for biological dynamics and biocommunications suggest that the quantum macroscopic coherent phenomena as Bose condensation and laser threshold could be present in living cells. A possible correlation between environmental primordial cosmic background radiation and Josephson experimental evidence is discussed.

4582. Sputtered nanodots: A costless method for inducing effective pinning centers in superconducting thin films

Authors: Crisan, A; Fujiwara, S; Nie, JC; Sundaresan, A; Ihara, H

Published: DEC 31 2001, APPLIED PHYSICS LETTERS, 79, 4549, DOI: 10.1063/1.1428632

A straightforward and cheap method for creating extended defects, strong pinning centers, in superconducting thin films is proposed. Clearly, by very short time (3-5 s) rf sputtering at suitable substrate temperatures, we deposited Ag nanodots on SrTiO3 substrates prior to the growth of superconducting thin films. The nanodots were studied by atomic force microscopy. Due to the lattice mismatch and/or chemical poisoning, on top of the nanodots the superconducting phase does not form, creating in this way extended and effective pinning centers which increase the critical current density of the film. The method was applied to (Cu, Tl)BaSrCa2Cu3Oy films grown by amorphous phase epitaxy. Thin films grown in similar conditions, with and without nanodots, were characterized by x-ray diffraction and ac susceptibility. The results show that the nanodots increased the critical current density more than one order of magnitude. (C) 2001 American Institute of Physics.

4583. Two-dimensional electron system in electromagnetic radiation field

Authors: Lungu, RP; Manolescu, A

Published: DEC 30 2001, INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 15, 4259, DOI: 10.1142/S0217979201008007

We consider a two-dimensional electron gas in the presence of a monochromatic linear polarized electromagnetic field, within the Floquet formalism. The Floquet states have a simple relation with the energy eigenstates in the absence of the field. Therefore the single-particle and the two-particle Green functions of the many-body system with Coulomb interactions, in the radiation field, can be formally calculated by the standard diagrammatic techniques, as for the conservative system. We derive the elementary excitations of quasi-particle type, the plasma dispersion relation, and the ground state quasi-energy, and we relate them to the corresponding results for the conservative system.

4584. Nondiverging vortex pinning barriers at low current densities across the putative elastic vortex-glass-vortex-liquid transition in YBa2Cu3O7-delta films

Authors: Miu, L; Basset, M; Jakob, G; Rodriguez, H; Adrian, H

Published: DEC 1 2001, PHYSICAL REVIEW B, 64, DOI: 10.1103/PhysRevB.64.220502

A detailed analysis of the electric field-current density (E - J) characteristics of YBa2Cu3O7-delta films across the putative thermally induced elastic vortex-glass-vortex-liquid transition predicted by the E(J) curve scaling reveals that the expected increase of the collective pinning barriers with decreasing J is cut off in the low-J region, signaling a dissipation process which involves the plastic deformation of the vortex system. The temperature and magnetic field dependence of the pinning barriers at low J does not change across the scaling-predicted glass transition line. For the investigated magnetic field range (0.5-7 T), over a relatively large temperature interval, in YBa2Cu3O7-delta films there appears a continuous crossover in a pinned plastic vortex assembly, rather than a thermally induced elastic vortex-glass-vortex-liquid transition.

4585. The stability of cadmium chalcogenide pigments in the process of laser cleaning of painted surfaces

Authors: Radvan, R; Popovici, N; Savastru, R; Ghica, C; Sava, F; Popescu, M

Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 902, DOI:

Pigments based on cadmium selenide sulphides and cadmium sulfides were analysed as regarding their structure and stability against the laser irradiation, a new technique for cleaning the painted surfaces in artwork restoration, The pulsed Nd:YAG laser radiation determines the effusion of some sulphur from the red pigment Cd(S,Se) and significant decrease of the average size of the crystallites. The color turns to dark red. For yellow pigment (CdS) no change of crystallite size was detected after laser irradiation.

4586. On the dynamics of surface layer in octylcyanobiphenyl-aerosil systems

Authors: Frunza, S; Frunza, L; Goering, H; Sturm, H; Schonhals, A

Published: DEC 2001, EUROPHYSICS LETTERS, 56, 807, DOI: 10.1209/epl/i2001-00591-8

A broadband dielectric study of the dispersions of silica spheres (Aerosil 380) in octylcyanobiphenyl (8CB) with densities between 0.083 and 10 g of silica per 1 cm(3) of liquid crystal (LC) is reported. High values of silica densities were achieved for the rst time to observe the behaviour of the LC monolayer on the surface of the silica particles. The relaxation characteristic of the bulk LC is noticed especially for the samples with low silica densities. Additionally, a slow relaxation was detected, even at temperatures for which the bulk LC is in the crystalline state. It was assigned to the surface layer of LC molecules. Remarkably, the temperature dependence of the relaxation rates for this slow process shows a behaviour typical for glass-forming liquids.

4587. Deep level defects in sublimation-grown 6H silicon carbide investigated by DLTS and EPR

Authors: Irmscher, K; Pintilie, I; Pintilie, L; Schulz, D

Published: DEC 2001, PHYSICA B-CONDENSED MATTER, 308, 733, DOI: 10.1016/S0921-4526(01)00887-0

6H-SiC bulk single crystals grown by physical vapor transport (PVT) were investigated by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). One of the observed deep level defects was identified as isolated tungsten on Si sites by EPR. The electron spin of 1 could be explained by W5+ (5d(1)). This is equivalent to the single positive charge state of a double donor when taking into account the Fermi level position in the n-type samples. The interpretation is also consistent with the DLTS detection of a W related deep level which showed a behavior of the capture of electrons and holes that hints at a double donor. In addition a tantalum related deep level is tentatively discussed. W and Ta were incorporated on electrically active sites in 6H-SiC only in low concentrations (2-4 x 10(4) cm(-3)) during crystal growth by PVT. (C) 2001 Elsevier Science B.V. All rights reserved.

4588. La2O3-doped BaTiO3 thin films obtained by pulsed laser deposition

Authors: Cernea, M; Mihailescu, IN; Martin, C; Ristoscu, C; Iliescu, M

Published: DEC 2001, JOURNAL OF MODERN OPTICS, 48, 2189, DOI: 10.1080/09500340108235509

La2O3-doped barium titanate (BaTiO3) thin films have been obtained by pulsed laser deposition. The structure and quality of deposited films were characterized by X-ray diffraction and scanning electron microscopy. A smooth surface was obtained when the films were deposited in 30 Pa ambient oxygen. The composition (elements and oxides) of the thin films were close to those of the target. The layer obtained by pulsed laser deposition from a target of BaTiO3 doped with 0.5 at.% La exhibits good dielectric characteristics: capacitance 88 pF, Curie temperature 59 degreesC and dielectrics loss, tan delta, 0.084.

4589. PbSe1-xTex thick thermoelectric films obtained by electrochemical deposition from aqueous solutions

Authors: Nedelcu, M; Sima, M; Stoica, T; Manea, AS; Lazarescu, MF; Visan, T

Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 914, DOI:

It is presented a study of PbSe1-xTex thick films electrodeposition on glassy carbon and ITO electrodes in acid solutions (0.1M HNO3), using cyclic voltammetry and rotating-disk techniques. Electrochemical impedance spectroscopy study of PbSe1-xTex film in 0.1M HNO3 is reported.

4590. Influence of the deposition configuration on the composition, structure and morphology of La0.6Y0.07Ca0.33Mn3-delta thin films obtained by pulsed laser deposition

Authors: Ghica, C; Valeanu, M; Nistor, LC; Teodorescu, V; Sandu, C; Ristoscu, C; Mihailescu, IN; Werckmann, J; Deville, JP

Published: DEC 2001, INTERNATIONAL JOURNAL OF INORGANIC MATERIALS, 3, 1256, DOI: 10.1016/S1466-6049(01)00153-2

We present a structural and morphological study on La0.6Y0.07Ca0.33MnO3-delta (LYCMO) thin films deposited by laser ablation onto MgO-buffered silicon wafers using two deposition configurations named on-axis and off-axis. All thin films have been deposited at high temperatures in an oxygen atmosphere. A comparative study between the on-axis and off-axis samples is performed by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The films are polycrystalline and show a columnar morphology. The off-axis sample shows a better crystalline texture, although slight compositional variations have been found. (C) 2001 Elsevier Science Ltd. All rights reserved.