National Institute Of Materials Physics - Romania

Publications

885 articles found

791. Synthesis and piezoelectric properties of nanocrystalline PZT-based ceramics prepared by high energy ball milling process

Authors: Miclea, C; Tanasoiu, C; Gheorghiu, A; Miclea, CF; Tanasoiu, V

Published: AUG-SEP 2004, JOURNAL OF MATERIALS SCIENCE, 39, 5434, DOI: 10.1023/B:JMSC.0000039260.82430.f9

Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300degreesC for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100degreesC and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d(33) of 550 pm/V, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed. (C) 2004 Kluwer Academic Publishers.

792. Structural, electrical, and photoelectrical properties of CdxPb1-xS thin films prepared by chemical bath deposition

Authors: Pentia, E; Draghici, V; Sarau, G; Mereu, B; Pintilie, L; Sava, F; Popescu, M

Published: 2004, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 151, G733, DOI: 10.1149/1.1800673

CdxPb1-xS (0 less than or equal to x less than or equal to 1) thin films were prepared on glass substrates using the chemical bath deposition method. The structural, electrical, and photoelectrical properties of the films were investigated, and all were dependent on the x value. For x > 0.5 (high Cd content), the films show a poor crystallinity and weak photoconductivity. For x < 0.5 (high Pb content), the films exhibit a good crystallinity, with an average size of the crystallites of 100 nm, and good photoconductivity. The threshold voltage of photoconductivity is shifted to lower wavelengths with increasing Cd content. The experimental results point toward possible ternary deposition on some composition ranges (near pure PbS or CdS); whereas, for the rest, the deposited film is rather a mixture of phases [not CdxPb1-xS but (CdS)(x)(PbS)(1-x)]. (C) 2004 The Electrochemical Society.

793. Radiation hardness of silicon - a challenge for defect engineering

Authors: Stahl, J; Fretwurst, E; Lindstroem, G; Pintilie, I

Published: DEC 31 2003, PHYSICA B-CONDENSED MATTER, 340, 709, DOI: 10.1016/j.physb.2003.09.238

Thermally stimulated current measurements of silicon particle detectors have been performed for defect characterization after high levels of gamma- and proton-irradiation. Two defects closely correlated with the detector performance were monitored: a deep acceptor (1) and a bistable donor (BD). In oxygen rich silicon the deep acceptor is largely suppressed while the BD generation is strongly enhanced. The influence of the starting material (standard float zone (FZ), oxygen enriched FZ, Cz, epitaxial silicon) on the formation of these two defects is discussed. Identification of the I-defect with the V2O complex, and of BD with the thermal double donor TDD2 is suggested. (C) 2003 Elsevier B.V. All rights reserved.

794. Second-order generation of point defects in highly irradiated float zone silicon - annealing studies

Authors: Pintilie, I; Fretwurst, E; Kramberger, G; Lindstroem, G; Li, Z; Stahl, J

Published: DEC 31 2003, PHYSICA B-CONDENSED MATTER, 340, 582, DOI: 10.1016/j.physb.2003.09.131

Isothermal and isochronal annealing experiments have shown that the I defect (the main cause for the changes in silicon diodes characteristics after high levels of gamma-irradiation) is stable up to 325-350degreesC. Possible reactions, which can explain the behavior of different defects formed during the annealing experiments, are discussed. All the experimental results concerning the I center (second-order irradiation induced defect, formed most likely via VO center, suppressed in oxygen rich material, high thermal stability) make it the favorite for being associated with the V2O2 complex. (C) 2003 Elsevier B.V. All rights reserved.

795. Superior radiation tolerance of thin epitaxial silicon detectors

Authors: Kramberger, G; Contarato, D; Fretwurst, E; Honniger, F; Lindstrom, G; Pintilie, I; Roder, R; Schramm, A; Stahl, J

Published: DEC 11 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 515, 670, DOI: 10.1016/j.nima.2003.07.021

For the LHC upgrade (fluences up to 10(16) p/cm(2)) epi-Si devices are shown to be a viable solution. No type inversion was measured up to 1.3 x 10(15) 24 GeV/c protons/cm(2) and the charge collection efficiency (CCE) remained close to 100%. For reactor neutrons CCE was measured to be 60% at 8 x 10(15) n/cm(2). Annealing measurements have shown that only moderate cooling during beam off periods would be necessary. As a tentative explanation for the superior quality of these devices, we assume that radiation-induced donor generation leads to compensation effects of deep acceptors. In the future, we will extend the experiments to fluences up to 10(16) p/cm(2) and use also different variants of the epi-Si material and device geometry. (C) 2003 Elsevier B.V. All rights reserved.

796. Field effect assisted thermally stimulated currents in CdS thin films deposited on SiO2/Si substrates

Authors: Lisca, M; Pentia, E; Saran, G; Pintilie, L; Pintilie, I; Botila, T

Published: DEC 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 852, DOI:

Field effect assisted Thermally Stimulated Currents (TSC) measurements were used to differentiate between electron and hole traps in CdS thin films deposited on SiO2/Si substrate. The electrode configuration was designed as for a pseudo-MOS structure, with drain and source contacts on the CdS film surface and using the Si substrate as gate electrode. Electron or hole traps will be favored to fill-up depending on the polarity of the gate voltage applied during illumination at low temperatures. Collection of the thermally released electrons or holes in the drain circuit will depend also on the polarity of the gate voltage applied during heating at constant rate. Comparing the results with those obtained in case of US films deposited on glass, it is possible to differentiate between SiO2/CdS interface traps and bulk CdS ones.

797. Bulk damage effects in standard and oxygen-enriched silicon detectors induced by Co-60-gamma radiation

Authors: Fretwurst, E; Lindstrom, G; Stahl, J; Pintilie, I; Li, Z; Kierstead, J; Verbitskaya, E; Roder, R

Published: NOV 21 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 514, 8, DOI: 10.1016/j.nima.2003.08.077

The influence of oxygen in silicon on bulk damage effects induced by Co-60-gamma irradiation has been studied in a dose range between 0.2 and 900 Mrad. The detector processing and oxygen enrichment were carried out in a common project by the Institute of Micro-sensors CiS using n-type high-resistivity FZ silicon (3-6 kOmega cm) with <111> and <100> orientation. Different oxygen concentrations were achieved by diffusion at 1150degreesC for 24, 48 and 72 h. This report on bulk damage effects is focussed on the observed changes in the reverse current, the effective space charge density N-eff extracted from C/V measurements and investigations using the transient current technique. A substantial improvement of radiation hardness concerning the development of the macroscopic properties was found for detectors manufactured on oxygenated material compared to standard material. It will be demonstrated that the change of the effective space charge density as well as the increase of the reverse current can be attributed to the creation of two deep acceptor levels and a shallow donor level. (C) 2003 Elsevier B.V. All rights reserved.

798. Results on defects induced by Co-60 gamma irradiation in standard and oxygen-enriched silicon

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: NOV 21 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 514, 24, DOI: 10.1016/j.nima.2003.08.079

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of Co-60 gamma irradiation, using Deep Level Transient Fourier Spectroscopy and Thermally Stimulated Current methods. The main focus was on differences between standard and oxygen-enriched material and the impact of the observed defect generation on the diode properties. Two close to mid gap trapping levels and a bi-stable donor level have been found to be responsible for the main macroscopic changes both in standard and oxygen-enriched float zone diodes. (C) 2003 Elsevier B.V. All rights reserved.

799. Second-order generation of point defects in gamma-irradiated float-zone silicon, an explanation for 'type inversion' (vol 82, pg 2169, 2003)

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: OCT 13 2003, APPLIED PHYSICS LETTERS, 83, 3216, DOI: 10.1063/1.1619226

800. Deep defect levels in standard and oxygen enriched silicon detectors before and after Co-60-gamma-irradiation

Authors: Stahl, J; Fretwurst, E; Lindstrom, G; Pintilie, I

Published: OCT 11 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 512, 116, DOI: 10.1016/S0168-9002(03)01884-9

Capacitance Deep Level Transient Spectroscopy (C-DLTS) measurements have been performed on standard and oxygen-doped silicon detectors manufactured from high-resistivity n-type float zone material with <111> and < 100> orientation. Three different oxygen concentrations were achieved by the so-called diffusion oxygenated float zone (DOFZ) process initiated by the CERN-RD48 (ROSE) collaboration. Before the irradiation a material characterization has been performed. In contrast to radiation damage by neutrons or high-energy charged hadrons, were the bulk damage is dominated by a mixture of clusters and point defects, the bulk damage caused by Co-60-gamma-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after Co-60-gamma-irradiation by C-DLTS are the electron traps VOi, CiCs, V-2(=/-), V-2(-/0) and the hole trap CiOi. The main difference between standard and oxygenated silicon at low dose values can be seen in the introduction rate of CiCs compared to CiOi. For highly oxygenated silicon the introduction of CiCs is fully suppressed, while the sum of the introduction rates g(CiCs)+g(CiOi) is independent on the oxygen concentration. (C) 2003 Elsevier B.V. All rights reserved.