National Institute Of Materials Physics - Romania

Publications

5840 articles found

4991. XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulse laser deposition

Authors: Teodorescu, VS; Blanchin, MG; Champeaux, C; Garapon, C

Published: 1998, ELECTRON MICROSCOPY 1998, VOL 2: MATERIALS SCIENCE 1, 658, DOI:

4992. Mossbauer spectroscopy applied to radioactive waste processing

Authors: Filoti, G; Kuncser, V; Prisecaru, I; Rotaru, P; Turcanu, CN

Published: 1998, HYPERFINE INTERACTIONS, 112, 204, DOI: 10.1023/A:1011076522131

Two original evaluations of the embedding process and of the hydration promotion in cements using only Mossbauer data have been proposed. Quantitative factors connected with the Mossbauer parameters and describing the hydration degree, the quality of the precipitate bonds in the cement matrix, as well as the influence of the additional organic components on the hydration process were found.

4993. On the photoluminescence decay in porous silicon films

Authors: Baltog, I; Ciurea, ML; Pavelescu, G; Mihut, L; Baibarac, M

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 626, DOI: 10.1117/12.312818

The photoluminescence (PL) decay measurements were performed on porous silicon films. It was observed that the two components of FL, one of them fast (ns) and the other slow (mu s or ms sometimes) have different contributions to PL signal, depending on the wavelength of the excitation light. The slow component of PL was in details investigated. Time decay cures for different excitation (337.1 nm, 470 nm and 550nm) and emission (550, 650, 700, 800 and 860 nm) wavelengths and also for different excitation intensities were taken. All decay curves were fitted with a stretched exponential. The slow component of PL was proposed to be attributed to the radiative recombination on surfaces.

4994. Ionic space charge limited currents in natural quartz crystal

Authors: Enculescu, I; Iliescu, B

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 266, DOI: 10.1117/12.312762

Arrhenius plots and current-voltage characteristics were studied for natural quartz samples, in different conditions of air-sweeping time, of temperature, of electrodes (with or without any source of positive ions). Some observations about the influence of the ionic space charge limited current are made. Some dependencies of ionic current versus voltage were found.

4995. Collective modes and the far-infrared absorption of the two-dimensional electron gas in a periodic quantizing magnetic field

Authors: Manolescu, A; Gudmundsson, V

Published: 1998, SUPERLATTICES AND MICROSTRUCTURES, 23, 1180, DOI: 10.1006/spmi.1997.0557

We investigate the far-infrared (FIR) absorption of a two-dimensional electron gas in a periodically modulated quantizing magnetic field. The magnetic field varies along only one spatial direction and the external time-dependent electric field is linearly polarized along that axis. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. The effects of the magnetic material on top of the heterostructure as a grating coupler is included in the time-dependent incident FIR electric field. We show that, similar to an electric modulation, the absorption can be directly correlated to the underlying electronic energy bands. In addition, the magnetic modulation leads to absorption spectra with a richer structure due to the quite different static response of the electron density to the modulation. (C) 1998 Academic Press Limited.

4996. Electronic properties of C-60 thin films

Authors: Mishori, B; Katz, EA; Faiman, D; Belu-Marian, A; Shapira, Y

Published: 1998, FULLERENE SCIENCE AND TECHNOLOGY, 6, 124, DOI: 10.1080/10641229809350188

The electronic structure of polycrystalline C-60 thin films has been investigated using surface photovoltage spectroscopy (SPS) and conductivity measurements. The films show n-type semiconductivity with an activation energy of approximate to 0.8 eV as found from the temperature dependence of the conductivity at high temperatures. The electronic structure emerging from our SPS results comprises a 1.6 eV photo-conduction gap, a mobility gap of about 2.25 eV and two gap states, a donor and an acceptor, at 0.35 eV and (1.0-1.1) eV, respectively, below the photo-conduction edge. The results indicate the possibility of the existence of band tails, extending into the optical gap of these films, as well as other deep gap states.

4997. Syntheses and structural study of trinuclear iron acetates [Fe3O(CH3COO)(6)(H2O)(3)]Cl center dot 6H(2)O and [Fe3O(CH3COO)(6)(H2O)(3)][FeCl4]center dot 2CH(3)COOH

Authors: Shova, SG; Cadelnic, IG; Gdaniec, M; Simonov, YA; Jovmir, TC; Meriacre, VM; Filoti, G; Turta, CI

Published: SEP-OCT 1998, JOURNAL OF STRUCTURAL CHEMISTRY, 39, 761, DOI: 10.1007/BF02903548

The structure of two trinuclear iron acetates [Fe3O(CH3COO)(6)(H2O)(3)]Cl . 6H(2)O (I) and [Fe3O(CH3COO)(6)(H2O)(3)][FeCl4]. 2CH(3)COOH (II) was determined by X-ray diffraction analysis. Crystals I and II are ionic and belong to the orthorhombic system with parameters a = 13.704(3), b = 23.332(5), c = 9.167(2) Angstrom, R = 0.0355, space group P2(1)2(1)2 for I and a = 10.145(4), b = 15.323(6), c 22.999(8) Angstrom, R = 0.0752, space group Pbc2(1) for II. The complex cation [Fe3O(CH3COO)(6)(H2O)(3)](+) has a mu(3)-O-bridged structure typical for trinuclear iron(III) compounds. As shown by Mossbauer spectroscopy, the iron(III) ions are in the high-spin state. In trinuclear cations, antiferromagnetic exchange interaction takes place between the Fe(III) ions with the exchange parameter J = -26.69 cm(-1) for N (Heisenberg-Dirac-Van Vleck model for D-3h symmetry).

4998. Crystallization of a-Si : H films by rapid thermal annealing

Authors: Szekeres, A; Gartner, M; Vasiliu, F; Marinov, M; Beshkov, G

Published: 1998, JOURNAL OF NON-CRYSTALLINE SOLIDS, 227, 957, DOI: 10.1016/S0022-3093(98)00263-4

The effect of rapid thermal annealing on the structural properties of hydrogenated amorphous silicon (a-Si:H) as a function of annealing time and temperature is studied by spectroscopic ellipsometry in the spectral region of 300-1200 nm, X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) methods. After annealing at 850 and 1050 degrees C, the a-Si:H films are predominantly amorphous and consist of two sublayers which contain a mixture of amorphous and crystalline silicon and voids, the volume fractions of which are temperature-dependent. Annealing of these a-Si:H samples at 1250 degrees C results in a completely crystallized and void-free structure. (C) 1998 Elsevier Science B.V. All rights reserved.

4999. Pulsed-laser and alpha particle irradiation effects in Fe-based glassy ferromagnets

Authors: Toacsan, MI; Barb, D; Sorescu, M; Constantinescu, B; Jeloaica, L

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 317, DOI: 10.1117/12.312772

A comparatively study of pulsed - laser and alpha particle irradiation effects in metallic glasses has been performed in order to understand the relationship between magnetic behaviour and select variations in the structural characteristics of alloy phases. Samples of Fe78B13Si9 and Fe66CO18B15Si metallic glasses were irradiated with a pulsed excimer laser (lambda=308nm, tau=10ns) and alpha particle beams (W = 2.8 MeV) using radiation doses of 10(16) and 10(17)cm(-2). Irradiation - driven changes in the magnetic anisotropy and phase equilibrium of alloy samples were studied by Mossbauer Spectroscopy and scanning electron microscopy. The evolution of phases and microstructure during the radiation-induced amorphous-to-crystalline transformations or revitrification depend on the specific irradiation and sample composition.

5000. Electrical properties of sandwich structures with aluminum nitride layers

Authors: Tanase, M; Morosanu, C; Dumitru, V; Tugulea, L; Tomozeiu, N

Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 224, DOI:

Electrical properties of adherent, low stressed aluminum nitride films prepared by magnetron sputtering have been studied. Arrhenius plots in the 100 degrees-170 degrees C range of temperature and transient current curves with different bias steps (af room temperature and 150 degrees C) have been performed. The conduction activation energy has been found and ifs dependence on subsequent annealings has been studied. A phenomenological conduction model at the ITO-AIN interface based on the shape of the transient curves has been elaborated The conditions of behaviour of AlN as a highly insulating layer (sputtering conditions, thicknesses, anealing temperatures) have been established.