National Institute Of Materials Physics - Romania

The way in which surface changes are transduced into a variation of an electrical parameter (often electrical resistance) depends on the surface oxidation level, material morphology its semiconductor behaviour, etc. Therefore, if one wants to understand more about the way in which gas-surface interactions affect the gas sensing properties of material, complex phenomenological and spectroscopic investigations are needed. Herein, by simultaneous DC and relative work function investigations we could explain the differences induced by the MOX semiconductor character (n and p-type) to the surface phenomena transduction mechanism.

An inciting and much debated subject in the surface enhanced Raman (SERS) studies is an unusual anti-Stokes Raman spectrum distinguished by an abnormal intensity, increasing with the vibrational wavenumber and some discrepancies with regard to the Stokes spectrum. We demonstrate that the abnormal anti-Stokes Raman emission on single walled carbon nanotubes and poly(3,4-ethylenedioxy thiophene) synthtetized electrochemically appears as a consequence of two corroborating effects: resonance, which occurs when the energy of the excitation light is near or coincident with the energy of an electronically allowed transition, and the SERS effect achieved by the excitation of surface plasmons. An abnormal intense Raman emission in the Stokes branch, reminiscent to a stimulated Raman effect, which increases exponentially with the intensity of exciting light is reported for the first time in the case of SWNTs.

We report on the versatility of pulsed laser deposition and radio frequency magnetron sputtering deposition methods to synthesize highly adherent bioactive hydroxyapatite thin layers on cranio-spinal implants as appropriate biofixation alternatives.

Nanocrystals of cubic ZnS (cZnS) doped with 02 % mol Mn2+, self-assembled into a mesoporous structure, have been prepared at room temperature by a surfactant-assisted liquid-liquid reaction The X-ray diffraction measurements confirm the formation of a sponge-like mesoporous structure built from ZnS nanocrystals with cubic (sphalerite) structure and pores of similar diameter of (1 8 +/- 0 2) nm. The Transmission Electron Microscopy (TEM) images show that the mesoporous structure consists of nanocrystals of cZnS with a tight size distribution centered around the average diameter value (21 +/- 0 3) nm The analysis of the observed Election Paramagnetic Resonance (EPR) spectrum demonstrates the presence of the Mn2+ activating ions at isolated sites in the mesoporous material, resulting in three types of paramagnetic centers called Mn2+(I), Mn2+(II) and Mn2+(III) The EPR spectrum of the Mn2+(I) center, attributed to substitutional Mn2+ ions at Zn2+ cation sites in the ZnS nanocrystals, exhibits the smallest linewidth values reported so far, reflecting an increased lattice ordering The high quality of the nanocrystals forming the mesoporous cZnS Mn, as reflected in a tight nanocrystallites size distribution and reduced crystallites lattice disorder, is attributed to the restraining effect of the self-assembling

The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results.

Multi-layered AlZnO thin films, with wurtzite - type structure and thickness up to 120 nm, as determined by x-ray diffraction and HRTEM, were grown on Si-SiO2 and glass substrates by the sol-gel method. Fluorescence spectroscopy measurements show that 0.5 at. % Al doping determines a blue shift of the emission band observed at 387nm in the undoped material. The room temperature conductivity increases when the number of layers increases, to reach a value of 3.70 (Omega.m)(-1) for a ten layer film. Results obtained by total energy first principles calculations performed on systems with chemical disorder are discussed in relationship with experimental data to account for the effect of Al on the conductivity.

Using europium as sensitive probe for both fluorescence and Mossbauer spectroscopy the morphological changes (local symmetry, covalence, ionicity) induced by the thermal treatments in the YVO(4) nanocrystals (synthesized by direct precipitation method) are put into evidence.

Silicon wafers have been submitted to hydrogen RF-plasma treatment in various experimental conditions The hydrogen RF-plasma treatment on Si wafers induces two kinds of effects surface corrugation and formation of structural defects below the wafer surface The structural defects resulted after the plasma treatments have been investigated by conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) techniques The specificity of the induced extended defects due to hydrogen decoration has been emphasized

New distributed multilayer microstrip structures are investigated in microwaves. The amplitude and phase responses are analyzed for different geometrical parameters, number of cells and dielectric constants of the dielectric layers. It is shown that the proposed structures exhibit left-handed properties in a frequency range near the resonance.

In this paper we present new results concerning the optical and morphologic properties of YVO4:Eu red nanophosphor prepared by a precipitation method and subsequently annealed in air at various temperatures. We monitored the morphologic changes induced by the thermal treatments using the optical spectroscopy (reflectance and luminescence spectra), XRD and electron microscopy. The annealing leads to an increase of the particle size and improvement of the order of the crystalline lattice of YVO4. The annealing at 800 degrees C produces the sample with the highest luminescence intensity.