Publications

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages. (C) 2011 Elsevier B.V. All rights reserved.

This paper presents some investigations on the properties of guanine (G) and cytosine (C) based heterostructures deposited on flexible substrates. The effects of two types of maleic anhydride-aniline derivatives (maleic anhydride-cyano aniline or maleic anhydride-2,4 dinitroaniline) buffer layer, deposited between indium tin oxide and (G) or (C) layer, on the optical and electrical properties of the heterostructures have been identified. The heterostructures containing a film of maleic anhydride-2,4 dinitroaniline have shown a good transparency and low photoluminescence invisible range. This buffer layer has determined an increase in the conductance only in the heterostructures based on (G) and (C) deposited on biaxially-oriented polyethylene terephthalate substrate. (C) 2011 Elsevier B. V. All rights reserved.

Chromium-doped titanium oxide thin films were investigated in the as-deposited state and after thermal treatment (723 K for 3 h in air). X-ray diffraction data revealed an improvement in film crystallinity induced by the thermal treatment. Extended X-ray absorption fine structure data revealed similar atomic neighboring around Cr atoms in both as-deposited and annealed samples. A lattice contraction of similar to 2% is observed in the annealed samples. The 67% enhancement of the amplitude of the Cr 1 s X-ray absorption fine structure pre-edge peak after thermal treatment, which is a sign of "dipole-forbidden" 1 s -> 3 d transitions, suggests strong alteration in the number of Cr 3 d vacancies, in spite of similar Cr local environment in the two kinds of investigated samples. We discuss here the Cr+ -> Cr4+ and Cr2+ -> Cr6+ changes induced by thermal treatment, and/or the evolution in local structures without inversion center. Refractive index dispersion spectra in the visible wavelength domain allowed us to compute the values of the dispersion energy, the single-oscillator energy and the coordination number of Ti atoms in both as-deposited and annealed samples. (C) 2011 Elsevier B. V. All rights reserved.

Thin films of As2S3 doped with Eu3+ were prepared by vacuum evaporation. It was measured the fluorescence spectra before and after a heat treatment at 180 degrees C for 45 minutes in inert atmosphere. After the heat treatment the transitions D-5(1) -> F-7(1), D-5(0) -> F-7(1) and D-5(0) -> F-7(2) were evidenced in the luminescence spectrum.

Tungsten films have a number of important applications. The techniques to produce quality films are very few and most of them use gases as precursors or as buffer. The Thermoionic Vacuum Arc (TVA) plasma is an original technique capable of producing pure, dense and very smooth Tungsten films of thicknesses from nanometers to tens of micrometers with no buffer gas or gas precursors. This paper presents characterisation of Tungsten films obtained by TVA in terms of composition and topography using XRF, XPS and AFM. The films studied are pure and contain a very thin surface oxide of WO(3). The influence of water vapors inherently present on the chamber walls to the film surface composition is also presented.

The in situ electrical properties and the catalytic activity of copper ferrite obtained by co-precipitation and thermal decomposition of polynuclear coordination compounds were studied in the propane oxidation reaction. The sample prepared by complexation had a better catalytic activity. Based on the conductivity data and the relative phase distribution in fresh and used compounds, the results are discussed in terms of the redox-type mechanism.

A series of TiO2 photocatalysts dispersed on SiO2, modified with metals (Mn, Cr, V) or nonmetals (N or S) or covered with Au nanoparticles were prepared by incipient wetness impregnation, impregnation with urea or thiourea, and deposition-precipitation, respectively. The photocatalysts where characterized by chemical analysis, X-ray diffraction (XRD), diffuse reflectance UV-Vis spectroscopy (DR-UV-Vis) and Fourier transform infrared spectroscopy (FTIR). The photocatalytic activity was checked in the photo-generation of hydrogen from sugar solutions. The nature of the modifying species was found to influence the photoactivity and N and S led to more effective catalysts than metals. This behavior was attributed to the fact the N and S are less effective in forming recombination centers compared with the metals. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In this paper we present electron paramagnetic resonance (EPR) and Mossbauer (transmission method, TMS and measurements in the scattering method, CEMS) experiments on Fe-57 (0.11at.%) doped nanocrystalline anatase-type TiO2, synthesized by a hydrothermal method. Different Fe3+ and Fe2+ ions positions, with various hyperfine interactions evidenced in Mossbauer spectra (MS), confirm a partial magnetic ordering at room temperature. The magnetic hyperfine fields in the TMS spectra, better resolved at lower temperatures, do not change essentially with temperature. The first CEMS measurements, carried out on iron-doped TiO2 nanoparticles, reveal a larger disorder in the surface particles layer. The temperature dependence of the double integral EPR spectral intensity, proportional with the sample susceptibility, shows an anomalous behaviour. It suggests the bound magnetic polaron (BMP) mechanism for the magnetic ordering.

Networks of dots made of As2S3 chalcogenide has been obtained by Vacuum Evaporation and Pulsed Laser Deposition from bulk glassy As2S3 by the adapted method of SCEV (screen evaporation method). A very thin layer of Eu2O3 was deposited from a different target in the final deposition process. After a heat treatment at 180 degrees C for 90 minutes in nitrogen atmosphere a structural transformation of the amorphous As2S3 to realgar (AsS) occurred in the PLD deposited dots and the network of dots develops a luminescence effect. (Received November 25, 2011; accepted December 2, 2011)

Thin (380-510 nm) films of a low silica content bioglass with MgO, B2O3, and CaF2 as additives were deposited at low-temperature (150A degrees C) by radio-frequency magnetron sputtering onto titanium substrates. The influence of sputtering conditions on morphology, structure, composition, bonding strength and in vitro bioactivity of sputtered bioglass films was investigated. Excellent pull-out adherence (similar to 73 MPa) was obtained when using a 0.3 Pa argon sputtering pressure (BG-a). The adherence declined (similar to 46 MPa) upon increasing the working pressure to 0.4 Pa (BG-b) or when using a reactive gas mixture (similar to 50 MPa). The SBF tests clearly demonstrated strong biomineralization features for all bioglass sputtered films. The biomineralization rate increased from BG-a to BG-b, and yet more for BG-c. A well-crystallized calcium hydrogen phosphate-like phase was observed after 3 and 15 days of immersion in SBF in all bioglass layers, which transformed monotonously into hydroxyapatite under prolonged SBF immersion. Alkali and alkali-earth salts (NaCl, KCl and CaCO3) were also found at the surface of samples soaked in SBF for 30 days. The study indicated that features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings.