National Institute Of Materials Physics - Romania

We present the fabrication and transport properties of a series of composites made of La2/3Sr1/3MnO3 and acrylamide-based copolymers. The most important result is the very narrow transition, of only 27 K, displayed by the peak that appears around the metal-insulator transition of the composites made with poly(acrylamide-vinylacetate). Although the amount of polymer is rather low, different copolymers change drastically the electric transport characteristics. Copyright (C) 2009

The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mossbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mossbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.

The output performances of a Nd:YAG laser passively Q-switched by Cr(4+):YAG saturable absorber are investigated function of temperature. Small variations in pulse energy and duration were observed over the 25 degrees C to 150 degrees C range. (C) 2009 Optical Society of America

The possibility to make surface measurements in the nano or micro range by Mossbauer spectroscopy using (151)Eu Mossbauer isotope is demonstrated. Measurements were made with a new flow detector in a backscattering geometry. With this detector it is possible to detect conversion electrons or low energy X-rays. An Eu(2)O(3) sample has been used. These measurements have been performed for the first time in Romania.

Fabrication of Au-Ti Schottky structure on GaAs semi-insulating wafer was related to an ultra-high vacuum deposition condition and low vacuum annealing in low vacuum and temperature range T=320-360 degrees C. There are presented representative I-V characteristics in dark and in different light (power levels). The spectral response has a maximum in Delta lambda = (850-950) nm corresponding to a band-to-band transition. The complex dependence of optical generated non-equilibrium carriers is related to the equivalent state density at the conduction band edge (in T(3/2) factor) and in exponential distribution factor exp (-(E-F)/kT).

This paper presents a study of two monomeric structures containing functional groups with different electronegativities [NH/NH-NH and NO2] and two different polymeric structures prepared by the copolymerisation of maleic anhydride and methylmethacrylate/maleic anhydride and vinyl benzyl chloride, and subsequent functionalization with 2,4 dinitroaniline. Thin films have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) and UV-VIS, FTIR, Raman and Photoluminescence Spectroscopy have been used to comparatively investigate the properties of the synthesised compounds. We have evidenced the second harmonic emission (SHG), process sustained by the asymmetry of the chemical structure, which is correlated with the crystallization in non-centrosymmeric structures.

The catalytic activity of hematite (alpha-Fe(2)o(3)) was studied in deep propane oxidation. Propane conversion to CO(2) was more than 90% at 400 degrees C in excess of oxygen. The AC electrical conductivity measurements performed in situ showed that at low temperature the surface conductivity is influenced by the presence of moisture in the feed which is adsorbed on the surface. Based on the conductivity data obtained in absence of oxygen coupled with information provided by Mossbauer spectroscopy, the results are discussed in terms of the redox-type mechanism.

ZnO:Co thin Films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). Increse of structural disorder and crystallite re-orientation are observed for cobalt doped samples (especially for those obtained at - 750 and at - 800 mV overpotentials). MOKE magnetometry revealed room temperature ferromagnetic behaviour only for ZnO:Co deposited at - 850 mV. These are the samples with the less cobalt content and lowest structural perturbation of the ZnO matrix by cobalt.

A theoretical relationship for the dissolution kinetics of thin chalcogenide films is proposed. The influence of light irradiation on the film dissolution is taken into account. The theoretical curves are in good agreement with the experimental dissolution results obtained for As2S3 thin amorphous films.

We report the formation of stable C-70 aggregate forms in o-dichlorobenzene/N-methyl-2-pyrrolidinone (DCB/NMP) and o-dichlorobenzene/acetonitrile (DCB/ACN) mixtures and their characterization by UV-VIS absorption spectroscopy and photoluminescence. As NMP acts on C-70 both as a solvent and reactant due to the unpaired electrons of the amidic nitrogen atom, molecular complexes (C-70/NMP) that aggregate slowly are formed by the binding of the NMP molecule to the fullerene cage. This interaction is seen in the UV-VIS absorption spectra of C-70 in DCB/NMP solvent mixtures by a gradual modification of the absorption spectra when increasing the NMP concentration. On the other hand, DCB and ACN combined form it typical solvent/non-solvent mixture favoring an intense aggregation of fullerenes. This yields to the C-70 clusters formations, having different size, similar to a precipitation process. Their characteristic is an abrupt variation in the absorbance appearing when the ACN is used in a greater extent. This different behavior of C-70 aggregation in DCB/NMP and DCB/ACN mixtures is also seen in their luminescence spectra recorded at different excitation wavelengths. While the PL spectra of C-70 solvated in DCB/NMP solution keeps almost the same modified shape irrespective the NMP concentration, the luminescence spectra Of C-70 in DCB/ACN mixture partially regains the powder C-70 PL signature as the ACN concentration is increased.