Publications

The fabrication and characterisation of surface acoustic wave resonators operating in the gigahertz frequency range are presented. The devices were fabricated on thin AlN layers deposited by magnetron sputtering on high resistivity (100) oriented silicon substrates. Using direct writing e-beam lithography, well defined interdigital transducers with 300 nm finger width and spacing have been obtained. On-wafer microwave measurements have demonstrated a narrow bandstop frequency characteristic with high rejection at approximately 5 GHz and an electromechanical coupling coefficient of 0.53%.

In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system.

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

A method for building photonic structures in As2S3 amorphous chalcogenide films has been developed. 2-D photonic configurations characterized by a regular assembly of rods (triangular lattice) or gratings with traces of micrometer period have been obtained. A femto-second laser has been used in photonic crystal registration. The simulation performed on these photonic configuration shows that the obtained chalcogenide structures could be efficient for operation in the infrared range around several micrometers wavelength.

Nitrogen is often used for doping TiO2 films to improve their photocatalytic properties in visible light. Multilayer TiO2 anatase films were deposited by sol-gel method on quartz substrate and thermally treated in O-2 and NH3 flow in 500-800 degrees C range. The effect of the annealing treatment (temperature and atmosphere) on the structural properties of TiO2 films was studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Nitridation causes the amorphization of the anatase tetragonal phase at 600 degrees C. The film re-crystallization into the cubic oxynitride phase is observed at 800 degrees C. EDX results confirms that the incorporation of nitrogen into the amorphous films takes place before thermally activated growth of the oxynitride phase and demonstrates that the relative O:N composition in the crystalline phase is dependent on the temperature of the thermal treatment.

The heterostructure Ag/As2S3 was deposited on glass substrate in two configurations: Ag/As2S3/glass and As2S3/Ag/glass. The effect of light emitted by a halogen lamp has been investigated by optical microscopy and X-ray diffraction. Particular morphological and structural aspects were revealed. Lateral diffusion rate of Ag has been determined.

In this paper, we present the anti-Stokes Raman scattering as a technique allowing investigations of materials at a nanoscale level. When the energy of the excitation light coincides with the energy of an electronic transition, a strong anti-Stokes Raman spectrum with respect to the prediction of the Maxwell-Boltzman (MB) law is regularly observed. Under a tight-focusing of the excitation light, the anti-Stokes Raman emission is reminiscent of Coherent anti-Stokes Raman Scattering (CARS). It has been detected on carbon nanotubes (CNTs), prototypes of nanometric materials, as well as on other compounds such as copper phthalocyanine (CuPc), poly(bithiophene) (PBTh), poly(3,4-ethylene dioxythiophene) (PEDOT), polyparaphenylene vinylene (PPV) layered as thin films on a metallic support in which are generated surface plasmons. We demonstrate that nanostructures by themselves can be of importance by generating non-linear phenomena that can be exploited for studying such materials and in particular carbon nanotubes. (C) 2009 Elsevier B.V. All rights reserved.

A paramagnetic Fe(III)- 2 deoxy D glucose (Fe-dGl) complex compound with Na(2)[Fe(2)(mu OH)(2)(2dGlc)(2))(2) (H(2)O)(2)Cl(2)] formula was synthesized and characterized by elemental analysis, IR and UV-VIS spectroscopy, thermal analysis TG-DSC, molar electrical conductivity as well as magnetic measurements and Mossbauer spectroscopy, with the aim of developing a new possible MRI contrast agent. The stability in physiological conditions and toxicity of the complex have also been established.

Crystals of potassium acid phthalate (KAP) doped with rhodamine 6G (Rh 6G) were grown by slow evaporation method from aqueous solutions. Crystals of good optical quality suitable for optical applications were obtained. Different concentrations of rhodamine 6G (10(-5) M, 2x10(-5) M, 5x10(-5) M and 10(-4) M in the growth solutions) were used in order to tune the optical properties of the crystals. Depending of the dye concentration, the absorption spectra of the dye-doped crystals show several bands in the range between 360 nm and 526 nm. The photoluminescence of the KAP crystals induced by the dye-doping reveals two emission bands peaking at 540 nm and 560 nm.

A new fluorine-free chemical solution deposition route has been developed for YBa2Cu3O7-x (YBCO) thin films. The precursor was formed by dissolving metal nitrates and citric acid in ethylene glycol. Polyethyleneimine was used to modify the solution. The preparation of YBCO thin films consisted of repeated dip coating, drying, heat-treating in air and annealing in flowing argon with a small addition of oxygen and with final treatment in pure oxygen. The films were characterized by XRD and SEM and show dominating and well-textured YBCO phase. The AC susceptibility and magnetization measurements reveal a critical temperature about 90 K and a high critical current density, comparable with that of pulse laser deposited films. The simplicity and high performance of the method may be attractive for large-scale superconducting applications.