Publications

Indium nitride is an attractive semiconductor material for optoelectronic applications, high-speed electronics and solar cells. We report successful deposition of polycrystalline InN thin films onto kapton polyimide flexible substrates by reactive RF magnetron sputtering method. The optical, structural and morphological characterization data are presented.

Star- and brush-polysiloxanes were synthesized via living radical polymerization using two different catalytic systems. The new compounds were characterized by H-1-NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) techniques. CuCl and 2,2'-bipyridyl proved to be the most efficient catalytic system. The type of catalytic system and the reaction conditions control the number of arms for star polymers or the grafted-chain density for brush polymers. The use of chloromethyl styrene as monomer or co-monomer yields homogeneous star- or brush-polysiloxanes, although chloromethyl styrene is an inimer system. The homogeneity of materials was verified by GPC and DSC (TOPEM) methods. For linear grafted polysiloxanes the molecular simulations reflect a tendency of chains to adopt globular conformation for high values of the branching density. The polysiloxanes grafted with styrene/chloromethyl styrene were modified with azobenzene in order to obtain systems able to react to the light stimuli. Rheological behavior of the polymer solutions were evaluated before and after irradiation with UV light. After the UV irradiation a significant viscosity increase was evidenced.

Magnetite nanoparticles coated with tyrosine and histidine were synthesized by in situ decomposition of the precursors-coordination compounds containing the aminoacids as ligands. All of the obtained compounds were characterized using infrared spectroscopy (FTIR), X-ray diffraction, Mossbauer spectroscopy, magnetic and thermal measurements. Data demonstrate the presence of the aminoacids chemisorbed on the surface of magnetite nanoparticles and their superparamagnetic character. (C) 2008 Elsevier B.V. All rights reserved.

The magnetron sputtering method was used to obtain layers of indium tin oxide or hydroxyapatite on glass fiber woven and on reference glass plates. The layers were characterized by scanning microscopy, UV-vis spectroscopy and conductivity measurements. Hydrophilic properties of the woven samples were investigated by optical microscopy following the behavior of a water droplet upon the each of the samples. The change of the drop profile in time due to wetting of the fabric leads to the wetting kinetics. The most efficient treatments to improve the hydrophilic/wetting properties of the glass fiber woven were found.

Blue cobalt aluminate was obtained by self-propagating combustion from the system 2Al(NO3)(3)center dot 9H(2)O : 1Co(NO3)(2)center dot 6H(2)O : nNH(2)CH(2)COOH. The precursor was characterized by elemental chemical analysis, IR and UV-Vis spectra and thermal analysis. The CoAl2O4 spinel was characterized by the X-ray diffraction, TEM, IR and UV-Vis spectra.

Single-walled carbon nanotubes (SWNTs) may be used in technological applications as individual entities instead of bundled tubes. The Raman signature of these two forms is still a controversial subject. The profile, peak position and relative intensity of the Raman band associated with the tangential vibration modes (G band similar to 1600cm(-1)) and radial vibration modes (RBM similar to 100-200cm(-1)) are the main parameters which can reveal the dispersion state of nanotubes. Resonant Raman scattering and absorption spectroscopy on SWNTs furnish complementary information concerning the efficiency of the nanotube dispersion in individual entities. (C) 2008 Elsevier B.V. All rights reserved.

Giant optical fields locally generated in nanoscale metal structures through the local excitation of surface plasmons underlie a variety of nonlinear optical processes. Using silver and gold rough metallic films, reproducible enhancements of the Raman signal on various materials including carbon nano-tubes have been demonstrated. In addition, an abnormal anti-Stokes Raman emission, reminiscent of Coherent anti-Stokes Raman Scattering (CARS), is accurately observed on nano-metric thin films. We demonstrate that under a tight focusing of the excitation light, a CARS-type emission, resulting from a wave mixing process between the incident laser light and Stokes Raman light generated by a SERS mechanism, is produced. The results which corroborate the CARS emission are the following: a square relation between the CARS signal intensity and the film thickness; a square relationship between the CARS signal intensity and the exciting laser intensity; a dependence of the CARS intensity on the numerical aperture (NA) of the microscope objective used for the detection of the anti-Stokes signal; a polarization ratio in the anti-Stokes side always greater in comparison with that measured for an usual Stokes Raman signal. We demonstrate also that this mechanism may contribute to a clear identification of the state of the observed nanotubes, i.e. in isolated or bundled forms, even when tubes are in powders. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The aim of this work was to study the influence of the sintering temperature and of the substitution level on the Curie temperature and on the magnetostriction coefficients for four series of cobalt ferrites sintered by conventional ceramic method. The microstructure of the samples was characterized using X-ray diffractometry and scanning surface electron microscopy. Vibrating sample magnetometry and strain gauge measurements were used to characterize the magnetic and magnetostriction properties. The study proves that a small amount of manganese substitution for iron decrease drastically the Curie temperature but in the same time decrease the specific magnetization and magnetostriction coefficient. Despite this drawback, the manganese substituted cobalt ferrites present the largest strain derivative. The maximum of the magnetostriction coefficient is also influenced by the stoichiometry of the cobalt ferrites. The magnetostriction coefficient of cobalt ferrite can be enhanced by substitution of small fraction of iron or cobalt by silicon or manganese, this implying the modification of the strain derivative as well as magnetostriction at lower magnetic fields. The maximum magnetostriction can be tuned by substitution levels and sintering parameters. (C) 2008 Elsevier B.V. All rights reserved.

Electrical memory elements based on Ge-Sb-Te pure and doped by Sn-Se have been obtained by pulsed laser deposition on special substrates covered by gold as well as on common glass. A set of electrical memory elements in a 4x4 matrix structure on the glass substrate has been produced. Devices with 3 and 10 memory elements have been constructed and tested for their memory properties. The special features of the voltage-current characteristics have been revealed.