National Institute Of Materials Physics - Romania

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.

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.

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.

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.

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.

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.

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.

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.

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.

We studied the chemical growth of calcium phosphate nanostructured coatings onto silicon wafers pre-covered with carbonated polycrystalline hydroxyapatite films. Silicon wafers were covered with hydroxyapatite thin layers by radio frequency magnetron sputtering and then immersed in 370 degrees C simulated body fluids for up to 20 days. Immersed structures were extracted every 2 days for studies by Fourier transform IR spectrometry. The chemically grown layers were further analyzed by X-ray diffraction and scanning electron microscopy. The growth kinetics of calcium phosphate deposits was monitored by estimating the area of phosphate, carbonate and water stretching bands of the recorded infra-red vibrational spectra. Sequential annealing in vacuum up to 950 degrees C was applied to elucidate the nature of incorporated water. Our studies revealed that the layers growing in simulated body fluid are rougher than initial hydroxyapatite interlayers, contain carbonates, include water in interlayer's voids and have therefore an increased biological activity for promoting faster implants integration with human bone tissues.