Publications

Glass-ceramics containing Er3+/Yb3+ codoped CaF2 nanocrystals have been prepared by using the controlled crystallization above 650 degrees C of the (Yb3+/Er3+) codoped CaF2-SiO2 xerogels. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanoctystals of about 16 nm size. For pumping at 973 nm, this glass-ceramics shows, besides green and red up-conversion luminescence, violet (at similar to 408 nm) and near-ultraviolet emission (at similar to 380 nm). The mechanisms responsible for the upconversion luminescence are presented and discussed. The fluorescence lifetimes of the metastable levels responsible for violet, green and red luminescence are measured and their quantum efficiencies are estimated. (C) 2013 Elsevier B.V. All rights reserved.

A complex structure of four double layers of Ag / As2S3 has been deposited by Pulsed Laser Deposition method on a glass substrate. The effects of thermal annealing on the structural and optical properties were investigated. An effect of layer mixing has been evidenced.

We have prepared complex multilayer films based on Barium stearate. The multilayer samples have been deposited by the Langmuir-Blodgett technique. The complex multilayers were also deposited on body sensor. The sample was then subjected to the illumination with UV light. We observed changes in the resistivity of the multilayer during the illumination

Tungsten-tantalum composites with 10 and 20 at.% Ta were prepared by ball milling W powder with Ta fibers and by consolidating the milled materials with spark plasma sintering. The composites were implanted at room temperature with He (30 key with a fluence 5 x 10(21) at/m(2)) and/or D+ (15 keV with a fluence 5 x 10(21) at/m(2)) ion beams. The materials were studied by scanning and high-resolution transmission electron microscopy, both coupled with energy dispersive X-ray spectroscopy, and by X-ray diffraction, Rutherford backscattering spectrometry and nuclear reaction analysis. The microstructure observations revealed that the milling operation resulted in severe fragmentation of the Ta fibers. Furthermore, during the consolidation process the Ta phase acted as oxygen getter and reduced the W oxide present in the original material. The surface of the tungsten-tantalum composites implanted with D+ remained essentially unaltered, while the materials implanted with He+ evidenced blisters on the Ta-rich regions. D retention in the composites increased with He pre-implantation. (C) 2013 Elsevier B.V. All rights reserved.

This paper is an overview of the very first results obtained on pure tungsten (W) and oxide dispersed strengthened (ODS) W alloys produced by the Metal Injection Molding (MIM) technique for fusion applications. An extensive mechanical and physical characterization was performed, together with microstructural material investigation. The reported work was accomplished within the framework of the European Fusion Development Agreement work program. The main objective was to develop suitable tungsten grades for structural and armor divertor applications in the future DEMO fusion reactor. (C) 2013 Elsevier B.V. All rights reserved.

Double perovskite Sr2FeMoO6 was prepared by two ways consisting in sol gel technique and solid-state reaction method. The resulting powders from gel and mixed oxides precursors showed microstructures consisting of very fine grains (0.5-0.8 mu m) and a crystalline perovskite structure. The structural and microstructural properties of the double perovskite Sr2FeMoO6 powders as-prepared and ceramics were compared. Tetragonal Sr2FeMoO6 pellets were prepared from the two powders by spark plasma sintering at: 1000, 1100 and 1200 degrees C and then annealing at 1200 degrees C, 2 h in 5%H-2/Ar. The pellets presented different magnetic characteristics. The saturation magnetization of the samples prepared by sol-gel is close to those prepared by conventional synthesis method. (C) 2013 Elsevier Ltd. All rights reserved.

Sol-gel chemistry within the pores of a polycarbonate template membrane was used for the preparation of Eosin Y-SiO2 hybrid nano- and microrods, using tetraethylorthosilicate [TEOS, Si(OC2H5)(4)] as the precursor in the presence of trifluoroacetic acid (TFA) catalyst. The ethanolic solution of Eosin-Y was added to the silica sal to trap dye molecules inside the SiO2 gel network during the gelation. Structural and morphological characterization using scanning electron microscopy (SEM) and luminescence microscopy have shown the formation of rods with 200 nm and 1.2 mu m diameter and about 30 mu m length, exhibiting luminescence properties. Spectroscopic characterization has shown that the luminescence is due to Eosin-Y molecule in the xerogel porous network, surrounded by a solvation shell given mainly by the water. (C) 2013 Elsevier B.V. All rights reserved.

This work presents a systematic investigation by X-ray photoelectron spectroscopy of the mechanisms of interface formation and band bending for Au/Pb(Zr,Ti)O-3 (PZT) layers grown on SrTiO3(001) with a SrRuO3 buffer layer, as function on the initial state of the PZT surface. After isolating the chemical effects, such as the formation of metal Pb at some surfaces, the evolution of the core levels with Au deposition allows one to simultaneously investigate the Schottky barrier formation and the built-in potential effects (charging induced by the static ferroelectric polarization). Areas of the sample with outwards P(+) and no polarization perpendicular to the surface P-(0) are identified for all samples. Only the freshly prepared sample exhibited inward polarization areas P(-). The built-in potential is on the order of 0.9 eV, while the Schottky band bending ranges from 0.2 to 0.6 eV towards lower absolute energies, therefore indicating that the work function of PZT exceeds that of Au deposited. We report also a chemically differentiate value of the built-in potential, manifested by a preferential distribution of the charge accumulated at the surface on Ti and O atoms. The O 1s and Ti 2p core levels manifest quite strong variations with the Au thickness for freshly prepared samples, resulting in shifts on the order of 2 eV towards lower binding energies. Au deposited on areas with an outward polarization is positively charged by the same potential as atoms from the PZT film (0.8-0.9 eV), whereas Au deposited on areas with an inward polarization forms a continuous grounded layer, which progressively pumps the accumulated charge and removes the polarization of these areas. (C) 2013 Elsevier B. V. All rights reserved.

As-grown n-4H-SiC/SiO2 capacitors exhibit anomalous capacitance-vs.-voltage (C-V) characteristics at low temperatures. Abrupt minima appear in the C-V curves at specific values of the gate voltages independent of the sample temperature, strongly suggesting the presence of resonant electron tunneling. We put forward a qualitative model where neutral donor states present at the SiC/SiO2 interface enable electron tunneling into distinct energy levels in the oxide. Numerical simulations based on this model show close agreement with the anomalous C-V characteristics observed experimentally. The model implies that under given conditions, i.e., the existence of a sufficient density of neutral donors at the semiconductor/oxide interface and empty electron states in the oxide layer, abrupt minima are in general to be expected during C-V measurements of metal-oxide-semiconductor capacitors. (C) 2013 Elsevier B. V. All rights reserved.

Electric and magnetic properties of symmetric and asymmetric Pb(Zr-0.2 Ti-0.8)O-3-CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25 nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization-voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell-Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure. (C) 2013 Published by Elsevier B. V.