National Institute Of Materials Physics - Romania

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5781 articles found

3541. Sequence of phases in the hydrothermal synthesis of zinc-doped magnetite system

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, V

Published: DEC 15 2007, MATERIALS CHEMISTRY AND PHYSICS, 106, 278, DOI: 10.1016/j.matchemphys.2007.06.001

Hydrothermal techniques have been used to synthesize samples of ZnxFe3-O-x(4) (x = 0.0-1.0) starting with ZnSO4 center dot 7H(2)O/FeSO4 center dot 7H(2)O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc-doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived and represented as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mossbauer spectroscopy data indicate the presence of magnetite and goethite at x <= 0.2, magnetite and zinc ferrite at x <= 0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content. (C) 2007 Elsevier B.V. All rights reserved.

3542. DLTS measurements of radiation induced defects in epitaxial and MCz silicon detectors

Authors: Honniger, F; Fretwurst, E; Lindstrom, G; Kramberger, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 108, DOI: 10.1016/j.nima.2007.08.202

n-Type epitaxial silicon layers of different thickness and resistivity, grown on highly Sb doped CZ-substrate by ITME (Warsaw), and n-type MCz silicon supplied by Okmetic (Finland) were used for the processing of planar diodes at CiS (Erfurt). For the epi-diodes a standard as well as a diffusion oxygenation process was employed. Irradiations had been performed with 26 MeV protons at the cyclotron of the Karlsruhe University and with neutrons at the TRIGA reactor of the Ljubljana University. Microscopic investigations using the DLTS method were done. The correlation of the IO(2i)-defect and the oxygen concentration was studied by a depth-profile measurement. The annealing behavior of the IO(2i)-defect at different temperatures was investigated and the activation energy extracted. (C) 2007 Elsevier B.V. All rights reserved.

3543. Radiation damage studies on MCz and standard and oxygen enriched epitaxial silicon devices

Authors: Fretwurst, E; Honniger, F; Kramberger, G; Lindstrom, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 63, DOI: 10.1016/j.nima.2007.08.194

N-type epitaxial layers of 72 mu m thickness and a resistivity of 150 Omega cm have been grown on highly Sb-doped Cz-substrates at ITME (Warsaw). The diode processing was performed at CiS-Erfurt. For comparison a batch of 280 mu m thick n-type MCZ wafers with a resistivity of >600 Omega cm from Okmetic (Finland) was added to the process run. Depth profiles of the oxygen and carbon concentration were measured via the SIMS-method on as grown epi-layers and after different device-process steps at CiS including an oxygen enrichment at 1100 degrees C for 24 h. For the MCz material the profiles were measured on untreated samples and after the full device process. Irradiation runs were performed with neutrons at the TRIGA reactor of Ljubljana up to a fluence value of 10(16) cm(-2). The development of the macroscopic device parameters (effective doping concentration and charge collection for a-particles) as function of fluence is presented for the standard and oxygenated epi-devices and compared with the MCz-diodes. The results are discussed in the frame of defect studies resulting from TSC-measurements. (C) 2007 Elsevier B.V. All rights reserved.

3544. Modelling spatial distribution of defects and estimation of electrical degradation of silicon detectors in radiation fields at high luminosity

Authors: Lazanu, S; Lazanu, I

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 168, DOI: 10.1016/j.nima.2007.08.206

The irradiation represents a useful tool for determining the characteristics of defects in semiconductors as well as a method to evaluate their degradation, a fact with important technological consequences. In this contribution, starting from available data on the degradation of silicon detector characteristics in radiation fields, these effects are explained in the frame of a model that supposes also the production of the Si-FFCD defect due to irradiation. The displacement threshold energies different for different crystallographic axes, considered as parameters of the model, are established and the results obtained could contribute to clarify these controversial aspects. Predictions of the degradation of electrical parameters (leakage current, effective carrier concentration and effective trapping probabilities for electrons and holes) of DOFZ silicon detectors in the hadron background of the LHC accelerator, supposing operation at -10 degrees C, are done. The non-uniformity of the rate of production of primary defects and of complexes, as a function of depth, for incident particles with low kinetic energy was obtained by simulations using some particular and very simplifying assumptions, suggesting the possible important contribution of the low-energy component of the background spectra to detector degradation. (c) 2007 Elsevier B.V. All rights reserved.

3545. Electric and magnetic response of Li-doped YBa2Cu3O7(LiF)(x) under neutron irradiation

Authors: Sandu, V; Aldica, G; Sandu, E; Nita, P

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3836, DOI:

We investigate the effect of neutron irradiation on the electric and magnetic properties, including the enhancement of the critical current density, of ceramics YBa2Cu3O7(LiF)(x) samples. The most important finding has been that the level of Li-doping is crucial for the postirradiation response. The irreversibility increases for more than two times in the samples with x <= 0.04 after neutron irradiation at 5 x 10(17) neutron S/cm(2) but less for higher concentrations. The effects of the irradiation on the electric transport and ac-susceptibility suggest a self-organization of the defects at low Li content and a uniformly space distribution for x >= 0.08.

3546. Structural investigations on yttria-doped zirconia nanopowdeirs obtained by sol-gel method

Authors: Vasile, BS; Ghitulica, C; Popescu-Pogrion, N; Constantinescu, S; Mercioniu, I; Stan, R; Andronescu, E

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3780, DOI:

The attractive properties of zirconia, particularly fracture toughness, wear resistance and chemical stability, have led to vast research efforts designed to investigate, characterize and develop such materials. Applications vary from structural, mechanical, biomedical to electrical, especially the fuel cells field. The current study is aiming at preparation and structural characterization Of 10% Y2O3 stabilized ZrO2 nanometric powders. The sol-gel method is known to be easy to use for producing various kinds of materials, structured at nanometric level, so was chosen for the elaboration of powders. Different thermal treatments were applied to the obtained materials, which were consequently investigated through thermal analysis, X-ray diffraction (XRD) scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characteristics Of Y2O3 doped zirconia powders are influenced by the processing parameters and proved promising for further applications in, for example, the Solid Oxides Fuel Cell field.

3547. Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate

Authors: Nelea, V; Morosanu, C; Bercu, M; Mihailescu, IN

Published: DEC 2007, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 18, 2354, DOI: 10.1007/s10856-007-3135-1

The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 degrees C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO2 film grew at the interface during annealing in moist air, while a TiO2 layer diffused into the HA films when directly sputtered at 550 degrees C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.

3548. Microwave dielectric properties of BaTi4O9-Nd2O3, BaTi4O9-Sm2O3 and BaTi4O9-WO3 ceramics

Authors: Cernea, M

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3794, DOI:

Barium tetratitanate (BaTiO9) powder, synthesized by coprecipitation method, was used to prepare BaTi4O9-Nd2O3, BaTi4O9-Sm2O3 and BaTi4O9-WO3 ceramics with microwave dielectric properties. The structure and microwave dielectric properties were studied. BaNd2Ti5O14 and BaSm2Ti4O12 single-phase ceramics were obtained from BaTi4O9:Nd2O3=1:1 and BaTi4O9:Sm2O3=1:1, respectively. A multiple phases ceramic containing mainly BaWO4 and small amounts of Ba2Ti9O20 and BaTi4O9 was obtained from BaTi4O9:WO3=1:1. BaTi4O9-Nd2O3, BaTi4O9-Sm2O3 and BaTi4O9-WO3, ceramics sintered at 1375 degrees C for 8.5 h in air, shown good microwave dielectric properties.

3549. Electrical characteristics of nano-PbS/SiO2/Si heterostructures obtained by chemical bath method

Authors: Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Botila, T; Negrila, C

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3802, DOI:

The PbS/SiO2/Si structures show a clockwise hysteresis of capacitance-voltage (C-V) characteristics. The loop width increases with temperature and sweep time. The conductance-voltage (G-V) characteristics also present a hysteresis effect with two bumps. Both characteristics show a strong shift with frequency. We show that these effects are determined by the positive mobile ions injected in the oxide region during the chemical bath deposition of PbS and by the high concentration Of Si/SiO2 interface states. The corresponding C-V and G-V characteristics are simulated and the main peculiarities of the experimental results are well reproduced by the modeled curves.

3550. Electrical conduction in initial field assisted sintering stages

Authors: Aldica, G; Khodash, V; Badica, P; Groza, JR

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3870, DOI:

Field Activated Sintering Techniques (FAST) are increasingly used to consolidate metal and ceramic powders. They combine application of a pulsed electrical current with external pressure to activate the densification process. The nature of electrical field/current interaction with powder systems is not clear yet. In this regard, in-situ transport measurements and microstructural analyses were carried out during pulsed current application in the FAST processing of Ni powders. Our experimental results were compared with existing electrical conduction theories and observed effects were relatively well explained qualitatively within these theories. Under electrical field it was confirmed that no voltage-current phase-shift occurs at elevated operating interfacial temperatures. For the field situation a higher applied pressure is decreasing the contact instability among particles contacts and of the sintering onset temperature. Microstructural investigations of the FAST-sintered samples indicate rather distribution of the higher density regions and a considerable increase of neck formation above 340 degrees C.