National Institute Of Materials Physics - Romania

The obtaining of a good ohmic contacts on the semiconductor material surfaces is strongly depending on the ability of the cleaning procedures to remove the native oxides and also, in the case of the compounds, to keep the surface stoichiometry. In this work, the XPS technique has been used in order to compare the efficiency of both, chemical etching and the Ar+ ion sputtering methods as to be suitable cleaning procedures in the case of n-GaP semiconductor compound surfaces preparation for the optoelectronic devices obtaining. The results have revealed some differences in the final surface composition/stoichiometry. The atomic ratio P/Ga within the outer layer of the single crystalline sample (similar to 100 angstrom) has been evaluated. The presence of residual of surface oxides was recorded after performing the chemical cleaning.

ZnO thin films were deposited by pulsed laser deposition (PLD) technique on optical glass substrate. Structural analysis by X-ray diffraction revealed a wurtzite phase ZnO, highly textured, with (002) planes perpendicular to the growth direction. They were optically characterized by absorption and transmission spectrometry. The wavelength dependence of the refractive index was extracted from transmission data by using a numerical fitting procedure.

Ferrite catalysts were prepared following two routes, i.e. the hydrothermal one and the calcination of an oxide mixture. In the first route sodium hydroxide, ferrous sulfate and the sulfate of the substituting ion (Mn, Ni) were used. The ferrites obtained using this route was NixFe3-xO4 (x = 0.5) and MnxFe3-xO4 (x similar to 0.65). Following the second route were prepared three samples: NiFe2O4, Ni0.5Zn0.5Fe2O4 and MnFe2O4. Two of them contain the corresponding ferrites while the latter is a presintered oxide mixture (Fe2O3-Mn2O3). All the samples were fully characterized using chemical analysis, X-ray fluorescence spectroscopy and EDX, nitrogen adsorption-desorption isotherms at -196 degrees C, X-ray diffraction (XRD), FTIR, scanning electron microscopy and XPS. The catalytic activity evaluation was made using a mixture of 1700 ppm vol. of toluene and air flowing at 100 ml min(-1) raising the temperature up to 600 degrees C in steps of 25 degrees C. Among these systems the sample representing the presintered Fe2O3-Mn2O3 mixture showed the highest activity. (C) 2008 Elsevier B.V. All rights reserved.

This paper presents a study of some functionalised copolymers thin films prepared on silicon and quartz substrates by matrix assisted pulsed laser evaporation ( MAPLE) method. Two polymeric structures have been synthesised by the copolymerisation of maleic anhydride and methyl methacrylate, respectively, maleic anhydride and vinyl benzyl chloride and their subsequent functionalisation with 2,4-dinitroaniline. UV-Vis, FTIR, Raman and photoluminescence spectroscopy have been used to investigate the influence on the properties of the films of different substrate temperature ( 150 degrees C and 250 degrees C), background N-2 pressure (5-30 Pa) and polymer concentration in target (2% and 3%). We have evidenced that this deposition process does not damage the chemical structure of the polymers. SEM investigations revealed the droplets type morphology of the polymeric films with thickness between 41 nm and 105 nm calculated from ellipsometric measurements. (C) 2008 Elsevier B. V. All rights reserved.

The characteristics of carbonic materials obtained by downstream deposition in a low pressure argon plasma beam injected with acetylene are reported. The influence of substrate temperature, presence of Ni catalyst and hydrogen in gas composition on the material properties is described. By increasing the substrate temperature, an enhanced order in the material is revealed by Raman spectroscopy, while FTIR measurements show a decreasing of the hydrogen content and the disappearing of sp(1) hybridized carbon in the deposit. The SEM and Raman investigation show a clear tendency of crystalline phases formation when hydrogen is assisting the deposition. (C) 2008 Elsevier B. V. All rights reserved.

Thin films based on two different metal-organic systems are developed by MAPLE and their nonlinear optical applications are explored. A complex of o,o'-dihydroxy azobenzene with Cu(2+) cation is found to organize as a non-central symmetric crystallite. A simple protocol is developed for the in situ fabrication of highly monodisperse copper-complex nanoparticles in a polymer film matrix of polyacrylic acid. The thin films were deposited on quartz substrates by MAPLE ( matrix assisted pulsed laser evaporation) using a Nd:YAG laser working at 355 nm. Atomic force microscopy (AFM), Fourier transform infrared ( FTIR), X-ray photoelectron spectroscopy (XPS), and optical second harmonic generation (SHG) were performed on the samples. The optical limiting capability of the nanoparticle-embedded polymer film is investigated. (C) 2008 Elsevier B. V. All rights reserved.

Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li2O-Al2O3-P2O5-(RE)(2)O-3, with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F-2 laser (lambda = 157 nm, iota approximate to 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV-VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications. (C) 2008 Elsevier B. V. All rights reserved.

Nitrogen-doped TiO2 nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 (vapors) and N2O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18 nm in case of the almost pure anatase sample to about 13 nm in case of the anatase-rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process. (C) 2008 Elsevier B. V. All rights reserved.

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0) Si and quartz substrates that were heated at temperatures from 300 to 500 degrees C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture. (C) 2008 Elsevier B. V. All rights reserved.