National Institute Of Materials Physics - Romania

Pbl(2) crystallite incorporated in optically transparent polyacrylamide and poly (vinyl alcohol) matrix have been studied by Raman scattering, photoluminescence (PL) at low temperature and Scanning Electron Microscopy (SEM). The small particles of Pbl(2) embedded in different host matrix were prepared by: i) cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide or poly (vinyl alcohol) and ii) by chemical reaction of KI and Pb(NO3)2 in aqueous polyacrylamide solution. In all cases, were identified hexagonal platelets of Pbl(2) and rods like particles. The rods are featured by a similar Raman spectrum and a specific green emission (cca 550 nm). Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the Pbl(2) layers of different molecular species. By compression the hybridized electronic level situated at the top of valence band, formed by the contribution.of the 6s and 5p states of Pb2+ and l ions, undergo a deformation that induces a weakness of the interaction between the lead ion and iodine electron within a layer so that the photoluminescence of intercalated Pbl(2) acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.

Lithium metallic colloids were studied in ion-implanted LiF crystals, irradiated with high energy He+ particles. The presence of metallic particles, displaying absorption bands at 420 and 460 nm due to the scattering of light on these particles, overlaps the absorption of M centers. The luminescence excited in this band, which is a superposition between the absorption of F-2 and F-3(+) centers, is reduced due to the metallic lithium particles, formed on the surface of the irradiated and at the end of the tracks of He+ particles, reducing the luminescence of the formed color centers. Diminution of the M band together with the growing of the 420 nm band versus irradiation doses, suggest a transformation of the color centers in small Fn-aggregates during the irradiation process, followed by a metallic conversion of Li ions.

One-dimensional structures having uniform diameters were prepared by electrochemical deposition using polycarbonate membranes as templates. Lead chalcogenides and ZnO tubes and rods growth processes were presented comparatively. The tendency of PbTe and PbSe semiconductors to grow as tubes both in membrane micro and nanopores was explained based on the absorption of lead ions on the pore wall.

Pure TiO2 and S-doped TiO2 sol-gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO2 porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.

The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe-Mn and Fe-Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe2+/Fe3+), manganese (Mn2+/Mn3+) and chromium (Cr3+/Cr6+) in the vitreous network. Mossbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe-Mn doped glasses, the percentage of Fe2+ is about 40% and a doubled iron content leads to an increasing of Fe2+ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe2+ percentage up to 56%. The occurrence of the tetrahedral or octahedral symmetry of Fe(2+)supercript stop ions bonded by O2- ions depends on the transition ion nature and Li+/Na+ ratio. Infrared absorption spectra of the pair transition ions-doped aluminophosphate glasses reveal optical phonons specific for the phosphate glass matrix.

The iron oxide nanoparticles and iron oxide nanoparticles coated with dextrin have been synthesized using aqueous solution of ferric and ferrous ions and mixtures of dextrin with sodium salt. The size of the iron-oxide nanoparticles is controlled by the concentration of sodium salt in the medium. An average size of iron oxide and iron oxide coated with dextrin was found by transmission electron microscopy (TEM). The iron oxide nanoparticles are nearly spherical with an average diameter of about 8.0 +/- 1 nm. The iron oxide nanoparticles coated with dextrin appear as cluster-like aggregates. The average diameter of these nanoparticles is about 5.1 nm. The attachment of the dextrin on the particle surface was confirmed by FTIR spectroscopy and thermogravimetric analyses (TGA).

We intend to prepare periodic multilayered structures for photonic applications. With this goal we have performed a study of some characteristics of SiO (x) -P2O5 films deposited by the sol-gel method on glass and ITO (InSnO (x) )-coated glass. The as prepared films were annealed to different temperatures (150 and 200 degrees C). The chemical composition of the samples was determined by X-ray Photoelectron Spectroscopy (XPS). The XPS results revealed the presence of P in the as-deposited films. The structural an optical properties were examined by Fourier Transform Infrared Spectroscopy (FTIR), Spectroellipsometry (SE) and UV Transmission Spectroscopy. IR spectra of the deposited films attest the interaction of an amorphous SiO2 with the H3PO4 used as a P-precursor. Refractive indices for individual SiO (x) -P2O5 determined from SE measurements show a densification of the layer structure with the increasing temperature in the thermal treatment. The UV transmission spectra revealed a lower transmission for the sol-gel SiO (x) -P2O5 films as compared to ITO/glass substrate. AFM images proved the densification of the films with annealing in agreement with the ellipsometric results.

By electrochemical deposition in a single nanopore membrane we fabricate Cu/Co layered single nanowires, that exhibit up to 10% magnetoresistance at room temperature. Single nanopore membranes are prepared by irradiating polycarbonate membranes with exactly one swift heavy ion, and by subsequent chemical etching of the single ion track. Both dc and pulsed electrodeposition of single wires consisting of Cu-Co alloy and Cu/Co multilayers respectively, are performed from a bath containing the two metal ions. By sputtering a gold electrode on the upper membrane surface, the single nanowire embedded in the flexible polymer foil is reliably contacted. While alloy wires exhibit anisotropic magnetoresistance (AMR), multilayer wires display current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) behavior. This demonstrates that both the fabrication and contacting methods are very suitable for the investigation of transport properties, without the necessity of lithographic processes and without manipulation of the nanowires. In addition, the method opens up many new possibilities for single nanowire-based sensors.

Thermoluminescence (TL) of Eu2+-doped BaFCl polycrystalline powders X- ray irradiated at room temperature show several TL peaks at 364 K, 408 K, 470 K, 524 K and 646 K. Thermally activated recombination processes responsible for TL have been studied using complementary techniques as TL and its bleaching, diffuse reflectance, X-ray excited luminescence (XL) and photostimulated luminescence (PSL). Experimental results indicate that F(Cr) centres are the dominant electron trap centres, the Eu2+-trapped hole aggregate centres playing the role of recombination centres. The 470 K and 646 K TSL glow peaks are assigned to the recombination inside the triple aggregates (Eu2+ - hole centre - F(Cl-) centre). The remaining 408 K and 524 K TL peaks are tentatively assigned to recombination between F centres and double aggregates (Eu2+ - hole centre). (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal nanoclusters of Ag and An were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.