National Institute Of Materials Physics - Romania

Publications

5840 articles found

4761. Optical absorption of Ag- centres in KCl: line shape calculation

Authors: Zota, S; Enculescu, M

Published: FEB 2000, PHYSICA B, 275, 343, DOI: 10.1016/S0921-4526(99)00762-0

The line shapes of the absorption spectra of KCl: Ag- are calculated at several temperatures in the range 80-300 K and are compared with the experimental results. The complete 12 x 12 Hamiltonian matrix of the system, which includes the linear electron-lattice interaction, was diagonalized directly and the integration has been performed by the Gaussian quadrature method. The results explain most of the characteristic features experimentally observed. (C) 2000 Elsevier Science B.V. All rights reserved.

4762. Diffraction-line shift caused by residual stress in polycrystal for all Laue groups in classical approximations

Authors: Popa, NC

Published: FEB 2000, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 33, 107, DOI: 10.1107/S0021889899013357

Analytical formulae for all Laue groups are derived, giving the dependence of the residual elastic strain measured by X-ray and neutron diffraction on the direction in the sample and on the Miller indices. These formulae are valid for isotropic polycrystals in the limits of the Reuss and Voigt approximations and are appropriate for Rietveld refinement.

4763. Metal clusters in metal/C-60 thin film nanosystems

Authors: Popescu, R; Macovei, D; Devenyi, A; Manaila, R; Barna, PB; Kovacs, A; Labar, JL

Published: FEB 2000, EUROPEAN PHYSICAL JOURNAL B, 13, 743, DOI: 10.1007/s100510050093

Structure of metal clusters and of the C-60 matrix in Au/C-60 and Cu/C-60 nanosystems was investigated by X-ray diffraction. Results support a charge-transfer-type interaction at the metal-C-60 interface, which affects the size distribution of metal clusters: favouring interstitial location of metal ions in the fullerite lattice.

4764. Finite-size effects in the magnetization of periodic mesoscopic systems

Authors: Erlingsson, SI; Manolescu, A; Gudmundsson, V

Published: FEB 2000, PHYSICA E, 6, 766, DOI: 10.1016/S1386-9477(99)00198-8

We calculate the orbital magnetization of a confined 2DEG as a function of the number of electrons in the system. Size effects are investigated by systematically increasing the area of the confining region. The results for the finite system are compared to an infinite one, where the magnetization is calculated in the thermodynamic limit. In all calculations the electron-electron interaction is included in the Hartree approximation. (C) 2000 Elsevier Science B.V. All rights reserved.

4765. Optical and structural differences between RF and DC AlxNy magnetron sputtered films

Authors: Dumitru, V; Morosanu, C; Sandu, V; Stoica, A

Published: JAN 24 2000, THIN SOLID FILMS, 359, 20, DOI: 10.1016/S0040-6090(99)00726-9

AlN films have been deposited by RF (1.78 MHz) and DC reactive magnetron sputtering (argon and nitrogen) on glass substrates at low temperatures (< 150 degrees C) and with 16, 21 and 30% nitrogen ratios. We have found optically and structurally distinguishable characteristics for films (both opaque and transparent), obtained using these two experimental methods. We suggest that these differences are due to plasma effects in the substrate during growth, resulting from the different ionic bombardment rates of the two sputtering modes. (C) 2000 Elsevier Science S.A. All rights reserved.

4766. Investigation of trapping levels in standard, nitrogenated and oxygenated Si p-n junctions by thermally stimulated currents

Authors: Pintilie, I; Petre, D; Pintilie, L; Tivarus, C; Petris, M; Botila, T

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 309, DOI: 10.1016/S0168-9002(99)00845-1

The trapping levels induced in p-n Si junctions by irradiation with 24 GeV proton were investigated using Thermally Stimulated Currents (TSC) methods in the 90-300 K temperature range. Several trapping levels, with activation energies between 0.27 and 0.57 eV, were put into evidence. The spatial distribution of the traps was investigated using different wavelengths for the light used to fill the traps. The results lead to the conclusion that the deepest trapping levels are not uniformly distributed in the volume of the sample. For the most important trapping level the average introduction rate was estimated to 0.9-1.2 cm(-1). The activation energy and the capture cross-section of this trapping level seems to depend on the impurity element introduced in Si. (C) 2000 Elsevier Science B.V. All rights reserved.

4767. Experimental evidence of deep electron and hole trapping levels in high fluence proton irradiated p-n Si junctions using optical charging spectroscopy

Authors: Pintilie, I; Tivarus, C; Botila, T; Petre, D; Pintilie, L

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 227, DOI: 10.1016/S0168-9002(99)00887-6

Optical charging spectroscopy (OCS) is first time reported as applied to p-n junctions. The existence of one deep trapping level for electrons and two deep trapping levels for holes was put into evidence, using this method, in proton irradiated p(+)-n-n(+) silicon structures. An analytical formula for the OCS discharging current for this type of structures was deduced. (C) 2000 Elsevier Science B.V. All rights reserved.

4768. The Mossbauer and magnetic resonances investigations of structural phase transitions in K2ZnCl4 crystals

Authors: Constantinescu, S; Grecu, MN

Published: JAN 2000, EUROPEAN PHYSICAL JOURNAL B, 13, 233, DOI: 10.1007/s100510050027

The experimental data carried out by Mossbauer and magnetic resonances investigations of the structural phase transitions in K2ZnCl4 crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential V(r), electric field intensity E(r) a,nd electric field gradient tensor, V-alpha beta(r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K Bites obtained by K-39-NMR methods in high temperature incommensurate phase (similar to Pnam symmetry). The experimental results obtained by Mossbauer and EPR methods in commensurate phase (Pna2(1) symmetry) of iron and copper doped K2ZnCl4 crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn2+ site.

4769. Crystal-chemistry aspects and electric-field-gradient (EFG) dispersion in Ca-gallogermanate-type structures studied by Mossbauer spectroscopy

Authors: Constantinescu, S; Tarina, D

Published: JAN 2000, EUROPEAN PHYSICAL JOURNAL B, 13, 81, DOI: 10.1007/s100510050011

The crystal field disorder in some trigonal germanates of the type X(3-y)Ln(y)Fe(2+y)Ge(4-y)O(14) (X = Ba, Sr; Ln = La, Nd; y = 0, 1) is studied by Fe-57 Mossbauer effect. The dispersion of the electric field gradient (EFG) at the octahedral sites of these compounds is investigated. A correlation of the experimental and calculated EFG data with some crystal-chemistry aspects is presented.

4770. Experimental investigation of the nonlinear optical response in Fe : PVA

Authors: Bulinski, M; Iova, I; Belea, A; Kuncser, V; Filoti, G

Published: JAN 2000, JOURNAL OF MATERIALS SCIENCE LETTERS, 19, 28, DOI: 10.1023/A:1006739412409