Publications

Single-phase Ba(Mg1/3Ta2/3)O-3 thin films were prepared by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) starting from a bulk ceramic target synthesized by solid state reaction. Atomic force microscopy, X-ray diffraction and spectroscopic ellipsometry were used for morphological, structural and optical characterization of the BMT thin films. The X-ray diffraction spectra show that the films exhibit a polycrystalline cubic structure. From spectroscopic ellipsometry analysis, the refractive index varies with the thin films deposition parameters. By using the transmission spectra and assuming a direct band to band transition a band gap value of approximate to 4.72 eV has been obtained. (C) 2010 Elsevier B.V. All rights reserved.

Potassium hydrogen phthalate (KAP) crystals doped with rhodamine 6G (Rh 6G) and polyvinylpyrrolidone (PVP) were grown by solution evaporation technique. Nucleation occurred without the use of seeds and optically transparent crystals were obtained. The grown crystals were characterized by XRD measurements performed on crystals and their powders, optical transmission and photoluminescence measurements. The influence of the dopants on the structural, morphological and optical properties of the KAP crystals was analysed. Dopants do not change the structure of the single crystals while the addition of PVP changes the morphology of crystals from pseudo-hexagonal to rhomb. Three new XRD reflections are observed in all single-crystal and powder XRD spectra and are probably (0 3 0), (0 4 0) and (0 5 0) lines. The UV cut-off and transparency of the crystals are not changed by doping. Dye-doped KAP crystals exhibit a strong emission band centred at 550 nm excited with 480 nm wavelength. For the dye-doped crystals the up-conversion was investigated and its second harmonic origins are proved using photoluminescence measurements. (C) 2010 Elsevier B.V. All rights reserved.

The present work reports the preparation of nanostructured ZnO nanorods in a hydrothermal-electrochemical process and preliminary attempt to fabricate a dye-sensitized solar cell using this material as photoanode. Synthesis of ZnO nanorods in solutions with and without eosin Y dye, used as nanostructuring agent, was studied. ZnO nanorod arrays were characterized by photoluminescence spectroscopy, scanning electron microscopy and X-ray diffraction analysis. Fabricated dye-sensitized solar cell comprised a photoanode prepared with nanostructured ZnO nanorods and eosin Y dye, a platinum counter electrode and an electrolyte consisting of 0.5M KI + 0.03M I-2 in acetonitrile/ethylene carbonate (v/v=1/4). Performance parameters of dye-sensitized solar cell were extracted from standard current-voltage characteristic.

Superconductor MgB2 has a significant potential for practical applications, but undesirable flux jumps in magnetization curves at low temperature and at moderate or intermediate magnetic fields prevent its widespread use. In the present work, we analyzed the flux-jumps tendency in MgB2 bulk doped with SiC, B4C and metallic Mg. Samples were prepared by field-assisted-sintering (FAST) as composites with up to three intercalated Fe-foils. Samples produced by FAST showed quite different phase structures clearly influencing pinning and thermo-magnetic instability features due to inhomogeneous materials structure or due to dopants. The largest flux jumps are observed in samples with high critical current density, as usually observed in conventional MgB2 bulks. However, jumps patterns are different and do not perfectly follow the jumps critical current dependence, especially for the samples with Mg-addition.

We investigated the influence of fullerene (C-60) addition on the superconducting parameters of MgB2 bulk samples obtained by spark plasma sintering (SPS). It was found that 1.5 wt% C-60 addition leads to the reduction of the critical temperature by a few K, whereas the magnetically determined critical current density increases by approximately one order of magnitude in an applied magnetic field H = 70 kOe at temperature T = 10 K. This indicates substitution of B by C in C-60 added MgB2 processed by SPS, contrary to some data reported in the literature obtained using conventional methods. For our relatively large specimens, the occurrence of macroscale flux jumps was observed over a wide (H, T) domain. The relaxation of the irreversible magnetization suggests that the macroscale flux jumps transform into microscale flux jumps with increasing H and T

Investigations on dielectric on compact resonators antennas with enhanced characteristics are described in this paper. The dielectric resonators were of (Zr(0.8)Sn(0.2))TiO(4) ceramic material (ZST). It is shown that the doping with Mg reduces the sintering temperature and provides a high dielectric constant, low loss and high thermal stability in microwaves. The coupling with an extra resonator can offer a substantial bandwidth enhancement. Moreover, antenna array with four antenna elements provides a higher gain and a more directive radiation pattern.

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+ (I), Mn2+ (II) and Mn2+ (III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+ (I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+ (II) and Mn2+ (III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.

We report on the synthesis of 700 nm thick bioglass thin films by magnetron sputtering from 45S5 bioglass targets in the argon atmosphere. The adhesion of films to Ti substrates increased 1 75 times when introducing an similar to 70 nm thick mixed glass-Ti buffer layer (BG(1-x)Ti(x) (x = 0-1)) with gradient of composition by co-sputtering. The morphological and structural properties of the films were studied by XRD, ETIR and microscopic techniques, showing an improvement after the two-hour thermal air treatment at 650 degrees C. We investigated in vitro the viability and proliferation of human osteoblast cells cultivated onto the surface of the films The osteoblasts spread over the surface adopting typical polyhedral shapes with numerous focal adhesion points and protrusions infiltrating deep into the films. We assigned this evolution to the improved mechanical properties and enhanced bioactivity due to the prevalent formation of combeite and wollastonite crystalline phases in the heat treated bioglass films (C) 2010 Elsevier B.V All rights reserved

Spin valve like AF/Fe/Cu/Fe (AF = Fe50Mn50 and Ir50Mn50) multilayer systems have been prepared by molecular beam epitaxy. Thin tracer layers enriched in the Fe-57 isotope were artificially grown at the AF/Fe and Fe/Cu interfaces and the interfacial atomic diffusion was observed via Fe-57 conversion electron Mossbauer spectroscopy. The results show that the atomic interdiffusion at all involved interfaces is lower in the IrMn based structures as compared to the FeMn based ones. (C) 2010 Elsevier B.V. All rights reserved

Short time spark plasma sintering at 1200 degrees C for 10 min and under a uniaxial pressure of 95 MPa followed by annealing at 1100 degrees C for 5 h is proposed for synthesis of high density (99%) Ba(Ti0.87Sn0.13)O-3 ceramic. Starting powder of 450 nm was obtained by co-precipitation, while the average grain size in the sintered ceramic was of 580 nm. X-ray diffraction analysis of the as prepared Ba(Ti0.87Sn0.13)O-3 samples indicated the presence of single phase BaTi0.87Sn0.13O3 developed in the BaTiO3 cubic structure. Samples have high relative dielectric constant of 5680 and low dissipation factor (tan delta = 0.009) at Curie temperature of 57 degrees C and 1 kHz, good tunability and ferroelectric properties. Remarkable is that these results are from some points of view different than for the conventionally processed samples with similar stoichiometry. Some ideas in this regard are presented and this suggests that SPS can be useful for expanded possibilities in the control of the properties. (C) 2010 Elsevier B.V. All rights reserved.