Publications

The Cyanobacterium Spirulina is commercialized for its use in health foods and for therapeutic purposes due to its valuable constituents particularly proteins and vitamins. The aim of the paper is to study the Spirulina platensis behaviour when it is electron beam irradiated for biological decontamination. Microbial load, antioxidant activity, enzymatic inhibition, electron spin resonance (ESR) and UV-Vis spectra were measured for doses up to 80 kGy. The results were correlated with doses in order to find where decontamination is efficient, keeping the Spirulina qualities. (c) 2005 Elsevier B.V. All rights reserved.

Second harmonic generation from n-doped GaAs(111)-A, GaAs(111)-B and GaAs(110) electrodes in sulfuric acid solution has been compared at an incident wavelength of 1064 nm over a potential range, where Faradaic process are excluded. In the p-in/p-out polarization configuration, the rotational anisotropy of the SH response reflects the symmetry of the crystal surface. The isotropic part of the response depends significantly on the applied electric field in the space-charge region, suggesting that the dominant part of the SH response is generated in the near-surface depletion region. The effects of the applied potential on the isotropic amplitude of the SH-signal show, however, that the high density of the surface/interface states at the Fermi level, revealed in impedance spectroscopy, may play an important role as well. (C) 2005 Elsevier Ltd. All rights reserved.

Piezoceramics with composition 0.46 Pb(Zr0.3Ti0.7)O-3 - 0.53 Pb(Ni1/3Nb2/3)O-3 have been synthesized by solid-state reaction at different temperatures. The density varied between 8.05-8.1 g/cm(3). The sintered samples have been chemically electroded with Ni and poled at 220C under an electric field of 3 kV/cm. The XRD spectra confirmed the formation of tetragonal crystalline phase with a tetragonal distortion c/a = 1.0125 which was decreased from a value of about 1.042 that corresponds to pure PZT with y = 0.3. Some minor traces of non-reacted precursor oxides such as Nb2O5 have been also found. TEM results confirmed the formation of tetragonal phase and revealed crystal grains with domains of different size, slightly disoriented from each other. Dielectric measurements performed between 20 degrees C and 300 degrees C at different frequencies between 100 Hz and 1 MHz revealed a broad dielectric anomaly at T-m = 118 degrees C (200Hz) which shifts to 127 degrees C at I MHz driving frequency. A dependence of T-m on sintering temperature has been observed. A thermal hysteresis is also found on heating and cooling. This shows that the samples present both relaxor and ferroelectric characteristics. High values of the dielectric constant are found both at room temperature (about 5000) and at T-m (about 18000). The dependence of dielectric and piezoelectric constants on sintering temperature has been found.

Ultra-thin (< 20 nm) lead zirconate-titanate films with Zr/Ti ratio of 20/80 have been deposited on single crystal MgO substrates by sol-gel techniques. Atomic force microscopy reveals a smooth surface consisting of pyramids or domes. The surface morphology is discussed in terms of a double-step growth process: epitaxial growth in the early stages followed by growth on screw dislocations. Measurements of the optical extinction spectra for the PZT (20/80) ultra-thin films are reported and modelled to extract the data on the energy gap.

Strain fields around dislocations in diamond and cBN have been quantitatively characterized at a sub nanometer scale. The combination of experimental high resolution electron microscopy (HREM) and image analysis using the geometric phase method provides an accurate determination of the local deformations and strain. The results of the strain analysis of the 60 degrees perfect dislocation in diamond and cBN are discussed. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Soft and hard type piezoceramic sintered samples were subjected to neutron irradiation in fluxes up to, 10(18) n/cm(2) and the changes of the basic properties brought about by irradiation were investigated. The results showed that intermediate irradiation levels of up to 10(15) n/cm(2) do not change significantly the properties, but higher levels changed them. Thus the electromechanical coupling factor, the dielectric permittivity and losses decreased while the mechanical quality factor increases with increasing neutron flux for both types of materials. Changes of the lattice constants a and c were also observed. The main defects produced by neutron irradiation are oxygen vacancies but they are not entirely responsible for the modification of the materials properties. Some other factors such as domain pinning and lattice deformation can contribute to the properties degradation.

The glassy, amorphous and disordered chalcogenide materials, important for optoelectronic applications, are discussed. The main optical and optoelectronic phenomena, specific to these materials are shown, and the applications based on these phenomena are evidenced.

X-ray absorption spectroscopy has been used to get information on the structure of chalcogenide glasses. The data analysis was focused on the near edge X-ray absorption spectrum. The experimental As and Se K-edge absorption spectra of thin films of As2Se3 and As4Se4 have been measured in Beijing synchrotron at the beam line, using a double crystal monochromator with Si (111) crystals. The near-edge absorption curves were resolved in two components: the strong white line at the energy threshold and the first oscillatory part following the white line at approximately 7-8 eV above the K-edge, which undergoes changes in shape and position as a function of the modifications in the atomic structure induced by the change of composition. The XANES characteristic for the two types of films allows to conclude that the local disorder around As and Se is different. The non-stoichiometric composition, As4Se4, exhibits more disorder than the stoichiometric one.

A layer of doped CdS nanocrystals was deposited on the surfaces of nanopores of polyethyleneterephtalate (PET) membranes. Optical absorption measurements were used to determine the bandgaps of the nanocrystals; CdS:Mn2+ and CdS:Mn2+:Cu+ show a blue and red shift, respectively, relative to the band gap of nanostructurated CdS. Photoluminescence spectra of the doped and undoped CdS samples exhibit wide bands covering the visible spectrum range.