Publications

X-ray diffraction and conversion electron Mossbauer spectrometry (CEMS) measurements of Fe87Zr6B6Cu1 samples in different steps of the crystallization process have been performed. The results have been compared with those obtained by means of the transmission Mossbauer technique. The X-ray diffraction patterns and CEMS spectra of the samples present systematically larger crystallized fractions than those corresponding to spectra obtained by transmission Mossbauer spectroscopy (TMS). As these techniques offer us information about different regions of the sample, the differences among the obtained results have been related to an inhomogeneity of the crystallization process into the sample induced by thermal treatments. (C) 2001 Elsevier Science B.V. All rights reserved.

Epitaxy of Fe on GaAs by the MBE technique has a long tradition in magnetism research. This paper deals with the growth of epitaxial Fe-GaN-Fe trilayer structures whose intriguing magnetic properties were exploited for the evaluation of GaN as a spin-dependent tunneling barrier. The trilayers were grown on semi-insulating (0 0 1) GaAs using an ultra-high vacuum deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma nitrogen source. (C) 2001 Elsevier Science B.V. All rights reserved.

The resistive transitions R(T) and the current-voltage (I-V) in fields up to 5 T were measured in a melt-textured YBa2Cu7-delta (YBCO) sample consisting of two single-grain domains separated by an inter-domain border, and in a single-grain sample cut from the same pellet and oxygenated in such conditions that ensure the optimum oxygenation of the grains. From comparing the two sets of results, we were able to suggest that the inter-domain border consists of oxygen-deficient YBCO with thickness smaller than 6 mum, having a slightly lower critical temperature, a higher anisotropy factor and without strong pinning centers. From applications point of view, our work shows that, for improving the superconducting properties of large multiple-domain melt-textured pellets. an oxygenation process much longer than that required for optimum grain properties is needed. (C) 2001 Published by Elsevier Science B.V.

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.

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.

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.

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.

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.

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.

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.