Publications

Upon 808 nm excitation, an intense broadband near-infrared emission from Cr4+ has been observed in 80GeS(2)-20Ga(2)S(3) chalcogenide glass-ceramics (GCs) containing Ga2S3 nanocrystals. The emission band peaking at 1250 nm covers the O, E, S bands (1000-1500 nm). The formation of Ga2S3 nanocrystals (similar to 20 nm) increases the emission intensity of Cr4+ by more than three times. The quantum efficiency of the present GCs is as great as 36% at room temperature. (C) 2012 Optical Society of America

ZnO-x%Eu2O3 (x=5 wt.%) binary oxide with straight strips morphology was successfully synthesized by hydrothermal route, using cetyltrimethylammonium bromide (CTAB) as template ZnSO4. Eu(NO3)(3)center dot 5H(2)O as inorganic precursors and ammonium hydroxide solution 28% NH3 for adjusting the pH to 11 value. The morphology, structure, photoluminescence and surface chemistry were investigated. The results highlighted that ZnO-Eu2O3 binary oxide shows straight strip morphology and crystalline framework indexed to wurtzite ZnO while Eu2O3 was detected as secondary phase. Surface chemistry revealed the presence of Eu3+. High sensor signal to 3 ppm NO2 together with its low sensitivity towards CO recommend this material as a good candidate in selective detection of NO2. (C) 2012 Elsevier B.V. All rights reserved.

The effects of 5 x 10(11) cm(-2 6+)I(127) ions of 28 MeV kinetic energy on high resistivity (100) Si were studied. The profile of primary defects was simulated. The defects produced by irradiation which act as traps were investigated. Thermally stimulated current measurements without externally applied bias were used, and for this the traps were charged by illuminating samples with 1000, 800, and 400 nm wavelengths. The discharge currents were recorded and modeled, and therefore the parameters of the traps were determined. The presence of I ions, heavier than Si, stopped into the target was modeled as a temperature independent electric field. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772015]

Using surface-enhanced Raman scattering (SERS) and Fourier transform infrared spectroscopy (FTIR) in the grazing angle incident reflection geometry, new data concerning the abnormal anti-Stokes Raman emission (AASRE) and the molecular orientation of poly(p-phenylenevinylene) (PPV) deposited on metallic supports of Ag and Au are reported. The particular dependencies of the anti-Stokes Raman intensity on the Raman shift, the sample thickness, and the incident pump intensity are highlighted in this paper. In the spectral range of 800-1000 cm(-1), the FTIR spectra of PPV films deposited on Ag and Au supports show a dichroism similar to that reported for the free-standing PPV film. Significant differences are reported in the spectral range of 1400-1700 cm(-1) for the s- and p-polarized FTIR spectra of PPV films deposited on Au and Ag supports. The annealing treatment at 110 degrees C of the PPV precursor solution in the presence of single-walled carbon nanotubes (SWNTs) induces a noncovalent functionalization of carbon nanotubes with the polymer molecules, as evidenced by a decrease of the radial breathing mode intensity and a decrease in the strength of AASRE. The process of noncovalent functionalization of SWNTs with PPV induces a change of the orientation angle of the transition dipole moment vector for the absorption band at 835 cm(-1). This fact is explained on the basis of the pi-pi* interaction between the phenyl group of PPV and the sidewall of the nanotubes.

Spectroscopic ellipsometry, X-ray diffraction and transmission electron microscopy experiments are employed to characterize aluminum nitride (AlN) thin films obtained by radio-frequency magnetron sputtering at low temperature (approximate to 50 degrees C). To understand the growth mechanism and to get in depth information of such films by using ex situ characterization techniques, the AlN thin film sample series were prepared for different sputtering times, while keeping constant all the other deposition conditions. The diffraction studies reveal a [002] oriented growth of the AlN thin films. The misorientation of this crystallographic axis to the normal to the surface reduces progressively with film growth. A nonmonotonic behavior of the AlN pseudo-refractive index versus deposition time indicates a complex depth profile of the AlN thin films optical properties. The difference in orientation dispersion of the [002] crystallite axis, the variation of defects concentration and each constituent atom density influence the refractive index evolution. Our interpretation validity was verified by producing and characterizing samples obtained at intermediate deposition time. The AlN thin films show also very good pull-out adherence values. (C) 2012 Elsevier B. V. All rights reserved.

The half-metallic properties of Ti2CoSn full-Heusler compound is studied within the framework of the density of states theory with the Perdew Burke Ernzerhof generalized gradient approximation (GGA). Structural optimization was performed and the calculated equilibrium lattice constant is 6.340 angstrom. The spin up band of compound has metallic character and spin down band is semiconducting with an indirect gap of 0.598 eV at equilibrium lattice constant. For the lattice parameter, ranging from 6.193 to 6.884 angstrom the compound presents 100% spin polarization and a total magnetic moment of 3 mu(B). (C) 2012 Elsevier Ltd. All rights reserved.

We were successful in synthesizing non-linear YBa(2)Cu(3)Ox whiskers, i.e. half loops or kinked shapes, which are promising candidates for solid-state devices based on the intrinsic Josephson effect and with improved electrical connections. We report on a complete characterization of their structural properties via a synchrotron nanoprobe as well as laboratory single-crystal diffraction techniques. This investigation allowed us to fully disclose the growth mechanism, which leads to the formation of curved whiskers. The superconducting properties are evaluated in comparison with their straight counterpart, revealing a strong functional analogy and confirming their potential applicability in superconducting electronic devices.

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations and produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60 degrees C and 80 degrees C on MOS capacitors and gate-controlled diodes irradiated to 5MGy and the annealing kinetics of oxide charges and surface current determined.

As synthesized mer-Alq(3) powder, obtained by wet chemical synthesis, has been subjected to different new characterization techniques such as Energy Dispersive X-ray, Cathodoluminescence and Scanning Electron Microscopy in order to identify their structural and photophysical properties. Other common techniques like X-ray diffraction, Raman and Fourier Transform Infrared spectroscopy have been involved in order to prove the formation of mer-Alq(3) compound. The vibrational spectroscopic properties were interpreted by using the output files from Gaussian software with B3YLP functionals and 6-311(d) basic sets. The growth kinetic of mer-Alq(3) nanocrystals in the alpha-phase has been evaluated by using the finite-size effects based on the Raman position peaks and their linewidths, which confirms the semiconductor character of the mer-Alq(3) compound. The XRD results suggest that the isothermal annealing increases the mer-Alq(3) nanocrystals, which modify the regular shape of typical spectral parameters from Raman peaks. (C) 2012 Elsevier B.V. All rights reserved.

Amination of bromobenzene with aniline was carried out on heterogeneous Au-TiO2 catalysts prepared using the deposition-precipitation method. The deposition of gold in loadings in the range 0.1-0.9 wt.% on titania occurred with the formation of gold particles with controlled size and oxidation state as demonstrated from TEM and XPS measurements. In addition, Raman and DR-UV-Vis investigation of these catalysts showed that the interaction of Au particles with the support stabilized the metallic state of gold. Catalytic results demonstrated that the conversion and selectivity depended on the gold-particle size and dispersion, while the mechanism of reaction was in direct relation with the reaction medium. Working in DMC, the solvent was playing the role of base. The advantage of working in DMC was avoiding the formation of KBr which is very difficult to be separated from the reaction products. HBr resulted as a by-product formed adducts with the coupling product, which was separated as crystals at room temperature by a simple filtration. However, in DMC, the reaction occurred with low selectivities. In dioxane, the presence of potassium ethoxide as base was mandatory. The reaction occurred with very high selectivities for moderate conversions. The conversion was limited by KBr released from the reaction. However, the use of the heterogeneous catalyst has the advantage of scavenger, since KBr becomes chemisorbed on the surface and could be simple removed by percolation and the catalyst can be reused. (C) 2012 Elsevier Inc. All rights reserved.