National Institute Of Materials Physics - Romania

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5975 articles found

4751. Classical polarons in a constant electric field

Authors: Meinert, G; Banyai, L; Gartner, P

Published: JUN 15 2001, PHYSICAL REVIEW B, 63, DOI: 10.1103/PhysRevB.63.245203

A classical model of electrons interacting with a longitudinal optical (LO) continuum phonon field via the Frohlich coupling is studied. Simulating a spatially homogeneous excitation by initially,distributing the electrons on a lattice, the solution of the many-body problem reduces to the evaluation of one nonlocal integro-differential (vector) equation, which can be solved numerically. According to the two parameters governing the behavior-electric field and coupling constant-two different regimes can be distinguished, a diffusive and a ballistic one. In the critical range of transition from one regime to the other the influence of the electron density becomes crucial. It is shown that the electrons-via the interaction with the phonon field-emit radiation in the terahertz range around the LO-phonon frequency.

4752. Developments for radiation hard silicon detectors by defect engineering - results by the CERN RD48 (ROSE) Collaboration

Authors: Lindstrom, G; Ahmed, M; Albergo, S; Allport, P; Anderson, D; Andricek, L; Angarano, MM; Augelli, V; Bacchetta, N; Bartalini, P; Bates, R; Biggeri, U; Bilei, GM; Bisello, D; Boemi, D; Borchi, E; Botila, T; Brodbeck, TJ; Bruzzi, M; Budzynski, T; Burger, P; Campabadal, F; Casse, G; Catacchini, E; Chilingarov, A; Ciampolini, P; Cindro, V; Costa, MJ; Creanza, D; Clauws, P; Da Via, C; Davies, G; De Boer, W; Dell'Orso, R; De Palma, M; Dezillie, B; Eremin, V; Evrard, O; Fallica, G; Fanourakis, G; Feick, H; Focardi, E; Fonseca, L; Fretwurst, E; Fuster, J; Gabathuler, K; Glaser, M; Grabiec, P; Grigoriev, E; Hall, G; Hanlon, M; Hauler, F; Heising, S; Holmes-Siedle, A; Horisberger, R; Hughes, G; Huhtinen, M; Ilyashenko, I; Ivanov, A; Jones, BK; Jungermann, L; Kaminsky, A; Kohout, Z; Kramberger, G; Kuhnke, M; Kwan, S; Lemeilleur, F; Leroy, C; Letheren, M; Li, Z; Ligonzo, T; Linhart, V; Litovchenko, P; Loukas, D; Lozano, M; Luczynski, Z; Lutz, G; MacEvoy, B; Manolopoulos, S; Markou, A; Martinez, C; Messineo, A; Mikuz, M; Moll, M; Nossarzewska, E; Ottaviani, G; Oshea, V; Parrini, G; Passeri, D; Petre, D; Pickford, A; Pintilie, I; Pintilie, L; Pospisil, S; Potenza, R; Radicci, V; Raine, C; Rafi, JM; Ratoff, PN; Richter, RH; Riedler, P; Roe, S; Roy, P; Ruzin, A; Ryazanov, AI; Santocchia, A; Schiavulli, L; Sicho, P; Siotis, I; Sloan, T; Slysz, W; Smith, K; Solanky, M; Sopko, B; Stolze, K; Avset, BS; Svensson, B; Tivarus, C; Tonelli, G; Tricomi, A; Tzamarias, S; Valvo, G; Vasilescu, A; Vayaki, A; Verbitskaya, E; Verdini, P; Vrba, V; Watts, S; Weber, ER; Wegrzecki, M; Wegrzecka, I; Weilhammer, P; Wheadon, R; Wilburn, C; Wilhelm, I; Wunstorf, R; Wustenfeld, J; Wyss, J; Zankel, K; Zabierowski, P; Zontar, D

Published: JUN 1 2001, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 465, 69, DOI: 10.1016/S0168-9002(01)00347-3

This report summarises the final results obtained by the RD48 collaboration. The emphasis is on the more practical aspects directly relevant for LHC applications. The report is based on the comprehensive survey given in the 1999 status report (RD48 3rd Status Report, CERN/LHCC 2000-009, December 1999), a recent conference report (Lindstrom et al, (RD48), and some latest experimental results. Additional data have been reported in the last ROSE workshop (5th ROSE workshop, CERN, CERN/LEB 2000-005), A compilation of all RD48 internal reports and a full publication list can be found on the RD48 homepage (http://cern.ch/RD48/). The success of the oxygen enrichment of FZ-silicon as a highly powerful defect engineering technique and its optimisation with various commercial manufacturers are reported. The focus is on the changes of the effective doping concentration (depletion voltage). The RD48 model for the dependence of radiation effects on fluence, temperature and operational time is verified: projections to operational scenarios for main LHC experiments demonstrate vital benefits. Progress in the microscopic understanding of damage effects as well as the application of defect kinetics models and device modelling for the prediction of the macroscopic behaviour was also been achieved but will not be covered in detail. (C) 2001 Elsevier Science B.V. All rights reserved.

4753. Fluctuation magnetoconductivity of BSCCO-2212 films in parallel magnetic field

Authors: Balestrino, G; Crisan, A; Livanov, DV; Manokhin, SI; Milani, E

Published: JUN 1 2001, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 355, 139, DOI: 10.1016/S0921-4534(00)01771-8

The in-plane (delta sigma (ab)(T,H)) and out-of-plane (delta sigma (c)(T,H)) components of the magnetoconductivity tenser of Bi2Sr2CaCu2O8+x films have been simultaneously measured in magnetic fields parallel to the film conducting planes (B less than or equal to 1 T). A negative c-axis magnetoresistance is measured for the first time in this geometry. Both delta sigma (ab) and delta sigma (c) are well described by the fluctuation theory in the temperature range T-c < T < T-c + 20 K, using a single set of microscopical parameters for both directions. The negative c-axis magnetoresistance in the field parallel to conducting layers is shown to be induced by the density of states Zeeman fluctuation contribution. (C) 2001 Elsevier Science B.V. All rights reserved.

4754. Selective polypyrrole electrodes for quartz microbalances: NO2 and gas flux sensitivities

Authors: Henkel, K; Oprea, A; Paloumpa, I; Appel, G; Schmeisser, D; Kamieth, P

Published: JUN 1 2001, SENSORS AND ACTUATORS B-CHEMICAL, 76, 129, DOI: 10.1016/S0925-4005(01)00600-1

Quartz microbalances were produced which have polypyrrole as a conductive polymer electrode. The polymer layers were operated as both electrode and sensitive material to detect the concentration of toxic gases. Tests with NO2 demonstrated detection limits below the MAK values at room temperature. It was also investigated the response to some other noxious compounds and to the total gas flux. The possible mechanisms associated with the sensor properties are pointed out and discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

4755. Chemically prepared nanocrystalline PbS thin films

Authors: Pentia, E; Pintilie, L; Matei, I; Botila, T; Ozbay, E

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 530, DOI:

PbS nanocrystalline thin films were prepared by Chemical Bath Deposition (CBD) technique. A comparative study between "standard" and "nanocrystalline" PbS thin films was performed. We denoted "standard" the PbS film with a good photosensitivity for to use as IR detector. This film was deposited after 1 hour from chemical bath containing reducing agent and Bi ions as doping element. The "nanocrystalline" film was obtained at shorter reaction time (after 17 minutes) from reducing bath without doping element. The other parameters: concentration of the reactants, pH, temperature were kept constant for the all depositions. The morphological properties of the films were determined by SEM analysis. Also, the electrical and photoelectrical behaviors were investigated for the both types of PbS films. The "nanocrystalline" film had a very high electrical resistance (10(10)-10(11)Omega/square) compared with the "standard" film (10(5)-10(6)Omega/square). Both types of films proved to be sensitive to the surrounding atmosphere, air or vacuum. Thermally Stimulated Current (TSC) measurement had shown the presence of trap concentration in the both cases, probably due to the large amount of disordered regions.

4756. Modelling of the structure and structural transformations in amorphous chalcogenides

Authors: Popescu, M

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 286, DOI:

Computer relaxed structural models of arsenic based chalcogenide glasses allowed to demonstrate that the atomic configurations in these materials are anisotropic with a strong tendency to extend as disordered layers. In the frame of these models the photostructural transformations and photoinduced anisotropy find a straightforward explanation.

4757. Structure and properties of chalcogenide glasses in the system (As2S3)(1-x)(Sb2S3)(x)

Authors: Sava, F

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 432, DOI:

The glass system (As2S3)(1-x)(Sb2S3)(x), 0 less than or equal tox less than or equal to0.65, has been studied by X-ray diffraction and microhardness measurements. The long-time Irradiation of the samples by ultraviolet rays has been carried out and its structural effect was investigated. The substitutional model and the microphase separation model have been discarded. A new intermediate model, whose main feature is the formation of mezoscopic Sb2S3 clusters, has been advanced.

4758. Visible light emission from Cd1-xMnxS nanocrystals

Authors: Ghiordanescu, V; Sima, M; Grecu, MN; Mihut, L

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 524, DOI:

The luminescence spectra of some Cd1-xMnxS nanocrystals have been measured at room and liquid nitrogen temperature. The Mn2+ ions give rise to a broad emission band centered at about 580 nm, between the emission bands of CdS host.

4759. UV irradiation effects in pure and tin-doped amorphous AsSe films

Authors: Popescu, M; Iovu, M; Hoyer, W; Shpotyuk, O; Sava, F; Lorinczi, A

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 306, DOI:

Pure and tin-doped AsSe amorphous films were investigated. The changes in the MRO induced by Sn were analysed be accurate profiling the first sharp diffraction peak (FSDP) in the X-ray diffraction diagram. A shift of FSDP as a function of tin concentration was observed. The structural changes induced by ultraviolet rays (lambda = 336 nm) for various time intervals of irradiation were revealed by small angle X-ray diffraction. It was revealed the formation of a special layer at the surface of the films. whose thickness increases during UV irradiation.

4760. The influence of BaZrO3 on the magnetic response of (Bi,Pb): 2223 high-temperature superconductors

Authors: Mihalache, V; Aldica, G; Popa, S; Nita, P; Crisan, A

Published: JUN 2001, JOURNAL OF SUPERCONDUCTIVITY, 14, 386, DOI: 10.1023/A:1011174321955

DC magnetization and AC complex susceptibility measurements on (Bi,Pb) : 2223 high-temperature superconductors impurified with various amounts of BaZrO3 are presented. The results are discussed in the frame of the critical state model. and the values of the inter- and intragranular critical current density as well as of the field for full penetration are estimated. The values of the intergranular critical current density are consistent with those obtained from transport measurements. The intragranular critical current density and the field for full penetration have similar values from both DC magnetization and AC susceptibility measurements. It was shown that, in the (Bi,Pb) : 2223 system. BaZrO3 impurification changes only the properties of the intergrain matrix, while the superconducting properties of the grains are not modified.