Publications

Magnetic titania nanoparticles covered/embedded in SiO2 shell/matrix were simultaneously manufactured by the single-step laser pyrolysis. The present study is a continuation of our previous investigations on the TiO2/Fe and TiO2/HMDSO (hexamethyldisiloxane) derived-systems. The aim of this work is to study the synthesis by IR (Infrared) laser pyrolysis of magnetic TiO2 based nanocomposites which implies many concurrent processes induced in the gas phase by the laser radiation. The dependence between characteristic properties and the synthesis parameters was determined by many analytical and complementary methods: XRD (X-ray diffraction) structural analysis, UV-vis (ultraviolet-visible) and EDAX (energy-dispersive X-ray) spectroscopy, TEM and HRTEM (transmission electron microscopy at low and high resolution) analysis and magnetic measurements. The results of analysis indicate the presence of disordered silica, Fe, alpha-Fe2O3 and mixtures of anatase and rutile phases with mean crystallite dimensions (in the 14-34 nm range) with typical character of diluted magnetic oxide systems and a lower bandgap energy (E-g = 1.85 eV) as compared with TiO2 P25 Degussa sample. (C) 2014 Elsevier B.V. All rights reserved.

In the present study the formation of lithium cobaltite using a modified Pechini aqueous sol-gel process was investigated. The gelling processes in the lithium-cobalt-citric acid system in 1.1:1:1 molar ratio was performed at 80 A degrees C using aqueous solutions of 0.25 mol/dm(3) of Co(NO3)(2)center dot 6H(2)O with Li(NO3)center dot 6H(2)O or Co(CH3COO)(2)center dot 6H(2)O with Li(CH3COO)center dot 2H(2)O, respectively. The study of the mechanism of gelling of transition metal ion Co(II) in aqueous medium in the presence of lithium ions and citric acid as chelating agents was approached using mainly UV-Vis and FTIR spectroscopic methods. The UV-Vis spectroscopy indicated that the Co(II) ions are in a tetragonal distorted geometry characteristic to a D-4h group symmetry in the solutions in the early steps of the gels formation. After gelling at 80 A degrees C it was observed that the symmetry of the Co(II) ions becomes octahedral (O-h). From the FTIR spectra based on the frequency separation between the antisymmetric stretching nu(as)(COO-) and symmetric stretching nu(sym)(COO-) vibrations, it was identified that the carboxylic groups are bond as a bridging ligands. Using X-ray photoelectron spectroscopy it was identified that the cobalt is present in both final gels as Co(II) ions and the citrate ions are covalently bonded to the cobalt ions. The thermogravimetric/differential thermal analysis showed the thermal stability of the studied gels is higher in the low temperature range for the gels prepared using acetates. Based on the thermal analysis the Li-Co-CA gels were calcinated at 700 A degrees C for 6 h and for each gel a monophasic LiCoO2 was obtained.

Both Spark Plasma Sintering (SPS) and conventional sintering were applied to obtain bulks of ledeburitic highly alloyed steels for tools fabrication. Powder mixtures of the component elements, of com-pounds or of powders obtained through ball milling of the chips resulting from the processing of parts from steels of interest were used. When compared with traditional technologies (casting and plastic deformation), SPS and the use of milled chips resulted in the formation of microstructures with a high degree of distribution homogeneity and dimensional uniformity of the carbides. As is well known, the improvement of these param-eters leads to the maximization of the functional properties of tools.

CuFe2-xCrxO4 spinel (0 <= x <= 2) powders were synthesized by a soft chemistry method-the gluconate multimetallic complex precursor route. The complex precursors were characterized by elemental chemical analysis, infrared (IR) and ultraviolet visible (UV-vis) spectroscopy, thermal analysis and Mossbauer spectroscopy. The oxide powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), IR, Raman and Mossbauer spectroscopy. It was shown that the structure, morphology and magnetic properties of the obtained spinel powders depend on the concentration of Cr3+ ion. The XRD of the chromium substituted copper ferrite powders calcined at 700 degrees C/1 h indicated the formation of a cubic spinel type structure for x=0.5, 1.0 and a tetragonal structure for x=0, 0.2, 2. The crystallite size ranged from 19 nm to 39 mm. The Mossbauer spectroscopy revealed the site occupancy of iron ions, relative abundance and internal hyperfine magnetic fields in both tetrahedral and cubic CuFe2-xCrxO4 spinels. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A series of niobium-modified aluminum hydroxide fluorides (denoted Nb@AIF(3)), prepared via a fluorolytic sol gel synthesis was investigated for the catalytic one-pot conversion of cellulose to lactic acid. The structure of the new acid catalysts is the result of the dispersion of niobium fluoride in an aluminum hydroxide fluoride matrix. The calcination of the catalysts at a relatively low temperature (350 degrees C) stabilized this structure. Catalytic performances in terms of lactic acid yields are directly correlated with the niobium content.

A rapid high sensitive method for determining the Faraday rotation of optical glasses is proposed. Starting from an experimental setup based on a Faraday rod coupled to a lock-in amplifier in the detection chain, two methodologies were developed for providing reliable results on samples presenting low and large Faraday rotations. The proposed methodologies were critically discussed and compared, via results obtained in transmission geometry, on a new series of aluminophosphate glasses with or without rare-earth doping ions. An example on how the method can be used for a rapid examination of the optical homogeneity of the sample with respect to magneto-optical effects is also provided. (C) 2015 AIP Publishing LLC.

This work is focusing on generation, time evolution, and impact on the electrical performance of silicon diodes impaired by radiation induced active defects. n-type silicon diodes had been irradiated with electrons ranging from 1.5 MeV to 27 MeV. It is shown that the formation of small clusters starts already after irradiation with high fluence of 1.5 MeV electrons. An increase of the introduction rates of both point defects and small clusters with increasing energy is seen, showing saturation for electron energies above similar to 15 MeV. The changes in the leakage current at low irradiation fluence-values proved to be determined by the change in the configuration of the tri-vacancy (V-3). Similar to V-3, other cluster related defects are showing bistability indicating that they might be associated with larger vacancy clusters. The change of the space charge density with irradiation and with annealing time after irradiation is fully described by accounting for the radiation induced trapping centers. High resolution electron microscopy investigations correlated with the annealing experiments revealed changes in the spatial structure of the defects. Furthermore, it is shown that while the generation of point defects is well described by the classical Non Ionizing Energy Loss (NIEL), the formation of small defect clusters is better described by the "effective NIEL" using results from molecular dynamics simulations. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

A new methodology for the accurate determination of the specific absorption rate of ferrofluids with magnetite nanoparticles of average size of about 10 nm subjected to alternative current magnetic fields is proposed. A simple numerical compensation of the heating rates by the cooling rates obtained at similar temperatures is employed. Comparisons of the as-obtained adiabatic heating curves with theoretical evaluations are discussed.

We investigate the properties of Dirac electrons in a finite graphene sample under a perpendicular magnetic field that emerge when an in-plane electric bias is also applied. The numerical analysis of the Hofstadter spectrum and of the edge-type wave functions evidence the presence of shortcut edge states that appear under the influence of the electric field. The states are characterized by a specific spatial distribution, which follows only partially the perimeter, and exhibit ridges that connect opposite sides of the graphene plaquette. Two kinds of such states have been found in different regions of the spectrum, and their particular spatial localization is shown along with the diamagnetic moments that reveal their chirality. By simulating a four-lead Hall device, we investigate the transport properties and observe unconventional plateaus of the integer quantum Hall effect that are associated with the presence of the shortcut edge states. We show the contributions of the novel states to the conductance matrix that determine the new transport properties. The shortcut edge states resulting from the splitting of the n = 0 Landau level represent a special case, giving rise to nontrivial transverse and longitudinal resistance.

Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 degrees C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.