National Institute Of Materials Physics - Romania

Publications

5840 articles found

4971. Self-consistent RPA retarded polaron Green function for quantum kinetics

Authors: Banyai, L; Haug, H; Gartner, P

Published: JAN 1998, EUROPEAN PHYSICAL JOURNAL B, 1, 213, DOI: 10.1007/s100510050173

We compute numerically the time dependent retarded Green function of the polaron within the self-consistent RPA approximation. The results show an approximately Gaussian behaviour at t = 0 changing at later times its concavity to an exponential decay? as it has been predicted in the approximate form of an inverse hyperbolic cosine function. The result contrasts with the non-selfconsistent RPA: where the exponential decay is only a transitory behaviour and the asymptotics is rather oscillatory. Our conclusions are significant in the context of the quantum kinetics with LO-phonons, where the transition from an intitially coherent scattering kinetics to a Markov kinetics with energy conservation is controlled by the time behaviour of the retarded Green function.

4972. A Mossbauer spectroscopy and magnetic study of FeRh

Authors: Rosenberg, M; Kuncser, V; Crisan, O; Hernando, A; Navarro, E; Filoti, G

Published: JAN 1998, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 177, 136, DOI: 10.1016/S0304-8853(97)00662-8

A Mossbauer and magnetic study of FeRh has been undertaken in order to understand better the remarkable properties of both melt-spun BCC and ball-milled FCC-phases of the anti-invar FeRh alloy. (C) 1998 Elsevier Science B.V. All rights reserved.

4973. EPR study of low temperature phase transitions in Mn2+ doped K2ZnCl4

Authors: Grecu, MN; Cevc, P; Blinc, R

Published: JAN 1998, SOLID STATE COMMUNICATIONS, 105, 15, DOI: 10.1016/S0038-1098(97)10041-2

The EPR spectra of Mn2+ doped K2ZnCl4 show an anomalously large broadening of the Zn site Mn2+ lines between 152.5 K and 145 K, i.e. just above the transition to the low temperature commensurate phase of A1a1 symmetry. The line broadening is related to a distribution of rotations of the ZnCl4 tetrahedra and supports the existence of a second incommensurate phase in this temperature range as reported by Gesi. (C) 1997 Published by Elsevier Science Ltd.

4974. QHE, magnetoresistance and disordered transport on 2D mesoscopic plaquettes

Authors: Aldea, A; Gartner, P; Nita, M

Published: JAN 1998, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 205, 356, DOI: 10.1002/(SICI)1521-3951(199801)205:1<351::AID-PSSB351>3.3.CO;2-Z

The transport properties of a rectangular mesoscopic plaquette in the presence of a perpendicular magnetic field are studied in a tight-binding model with randomly distributed traps. The longitudinal and Hall resistances are calculated in the four-probe Landauer-Buttiker formalism which accounts automatically both for the quantum coherence and the trapping-induced localization. The localized character of eigenvectors and the specific aspect of the density of states at a given magnetic flux are correlated with the behaviour of the mentioned resistances as function of the Fermi energy. The Hall insulator and quantum Hall regimes are evidenced. The magnetic field dependence of the configurational averages of the longitudinal and Hal; resistance is studied in a purely quantum-mechanical approach. Both, negative and positive magnetoresistances are found.

4975. On the crystal-to-mesophase phase transition in copper(II) salts of even-chain fatty acids

Authors: Fausto, R; Duarte, MLTS; Moita, MFR; Frunza, L; Beica, T; Frunza, S

Published: 1998, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 53, 139, DOI: 10.1023/A:1010111519530

The phase transition from the solid state to the liquid crystal state was investigated for the copper(II) salts of the fatty acids with 10, 12, 14, 16 or 18 carbon atoms in the chain, by measuring the temperature dependence of the conductance and capacitance of a cell containing the material under investigation. The temperatures deduced from these dependences agree reasonably with those found by DSC measurements and with those to be found in the literature. Differences in dielectric behaviour between the samples are qualitatively discussed.

4976. On the passivation of the metallic surfaces from the nuclear plant water circuits

Authors: Filoti, G; Kuncser, V; Palade, P; Micu, IF; Crisan, O

Published: 1998, HYPERFINE INTERACTIONS, 112, 38, DOI: 10.1023/A:1011063905776

Samples obtained from the hot conditioning and hot performance procedures have been investigated by GEMS. Various types of substrates were considered. The surface phases were assigned to magnetite, alpha-Fe, wustite and to spinel solid solutions. The data have been analyzed taking into account the compound stoichiometry, the number of iron unequivalent positions appeared in each identified phase and the relative ratio of the formed products.

4977. On polyaniline - Polyvinylchloride blends

Authors: Chipara, MI; Munteanu, I; Notingher, P; Chipara, MD; Romero, JR; Negreanu, B; Panaitescu, D

Published: 1998, PROCEEDINGS OF THE 1998 IEEE INTERNATIONAL CONFERENCE ON CONDUCTION AND BREAKDOWN IN SOLID DIELECTRICS - ICSD '98, 374, DOI: 10.1109/ICSD.1998.709303

4978. Elastic stress relaxation in TiN and ZrN hard coatings

Authors: Manaila, R; Biro, D; Barna, PB; Popescu, R; Fratiloiu, D; Adamik, M; Devenyi, A

Published: 1998, COST 516 TRIBOLOGY SYMPOSIUM, 180, 324, DOI:

4979. Investigation of deep impurity levels in high resistivity silicon using optical charging spectroscopy

Authors: Botila, T; Brancus, D; Pintilie, I; Pintilie, L; Petre, D

Published: 1998, DEFECT RECOGNITION AND IMAGE PROCESSING IN SEMICONDUCTORS 1997, 160, 296, DOI:

The Optical Charging Spectroscopy (OCS) was applied for the first time to investigate the trapping levels in high resistivity silicon irradiated with neutrons. An analytical formula for the OCS discharging current has been obtained. The theoretical and experimental results proved that the OCS is more sensitive than the usual Thermally Stimulated Currents method.

4980. Degradation effects in pulsed AlGaAs large optical cavity (LOC) structure laser diodes

Authors: Ghita, RV; Vasile, E; Cimpoca, V; Baltateanu, N

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 80, DOI: 10.1117/12.312670

High power pulsed laser diodes are of interest due to their potential use in medicine and peculiar applications. This paper presents failure analysis for catastrophic damage in GaAs/AlGaAs LOC pulsed laser devices. There is presented failure decrease of optical power as Ig (P/P-0) = f(t) where Po is initial power, P actual power, t-operating time. The damaged devices were investigated by optical and scanning electron microscopy (SEM) and there was performed a electron dispersion spectroscopy (EDS) analysis These experiments advanced the idea of dividing catastrophic degradation in three types, respectively: 1-catastrophic optical mirror damage (COMD), 2- catastrophic damage due to major mechanic defects (CDMMD), 3-catastrophic damage due to metal migration (e.g. Au) (CDMM). There was established an experimental criterion to characterise catastrophic damage.