National Institute Of Materials Physics - Romania

The iron oxide-based nanomaterials have a great importance because of their impact on a wide number of industries. They have many properties and applications in domains as: environmental protection, biomedical, catalysis, information displays and electronics. In order to avoid the tendency of nanoparticles to aggregate, they are often included in sol-gel derived silica matrices, thus being also ensured a homogeneous dispersion of the ultra-fine metal oxide particles in the host matrix. The reasons of the attempt are both an economic and a non-pollutant one, tacking into account the fact that it is well known that aqueous silica sol is cheaper and less toxic than TEOS. The Fe3O4 was introduced in the reaction mixture as aqueous suspension. A final iron content related to SiO2 of 3% wt. was chosen for the prepared nanocomposite. Thermal analysis, IR spectroscopy, XRD and TEM methods have been used for the structural characterisation,. Some experiments of water depollution (from As) have been proceeded using the prepared Fe3O4-SiO2 nanocomposite.

Some FexOy-SiO2 composites were prepared by the colloidal and alkoxidic route of the sol-gel method. The dried gels were thermally treated and the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorption (IR) spectroscopy, magnetic susceptibility measurements and Mossbauer spectroscopy. Nanoparticles of gamma and /or alpha iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the thermal treatment. It was observed that the particle sizes and the thermal stability of the iron oxide phases strongly depend on the preparation method. At temperatures above 400 degrees C, the gamma-phase begins to transform to the alpha-phase.

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

Porous membranes containing cylindrical pores with diameters ranging from a few tens of nanometers to a few tens of micrometers were prepared by using the ion track technique. Swift heavy ions (e.g. Au with 11.4 MeV/nucleon specific energy) were used for creating the ion tracks in polycarbonate foils. Etching was performed using an aqueous solution of NaOH containing methanol. The growth of the alkali-halides micro- and nanorods was performed by evaporation from a saturated solution. The rods were imaged using scanning electron microscopy. The method opens up the possibility of growing nanostructures with applications as nanolaser media or nanoscintillators.

We used the template method to prepare CdTe wires with diameters ranging from 80 nm to 1 mu m. As templates we used polycarbonate and polyethilene tereplitalate ion track membranes and as the method of filling the pores of such membranes we employed electrochemical deposition. The conditions (i.e. bath composition and deposition potential) necessary to obtain the stoichiometric composition of the semiconductor were found. Scanning and transmission electron microscopy were employed for morphological characterization of the nano and microwires. Energy dispersive X-ray analysis was employed for determining the Cd/Te ratio. Selected area electron diffraction was employed for structural measurements. Reflection spectroscopy measurements were performed on nanowire arrays for determining the band gap of the deposited nanostructures. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Manganese and copper doped ZnO films and nanowire arrays were prepared by cathodic electrodeposition from aqueous solution. The electrochemical process was examined by linear voltammetry and the morphology and the composition of obtained semiconductor were observed by SEM and EDX measurements. Optical absorption spectra indicated the presence of copper in ZnO: Mn: Cu nanowire arrays as Cu2+ ions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report in this contribution on the photosensitization effect of ZnO nanostructured thin films with copper-phthalocyanine (CuPc). ZnO films were prepared by pulsed laser deposition (PLD), on optical glass substrates, covered with 300 nm thick ITO films. The structure and morphology of ZnO films were optimized for photovoltaic-cell applications by controlling the growing conditions. ZnO films (wurtzite type) were (001) preferentially oriented in the growth direction. Organic dyes were vacuum sublimated on ZnO films, and subsequently a 300 nm thick copper film was vacuum sublimated on top of the structure, acting as an ohmic contact. Action spectra of ITO/ZnO/CuPc/Cu photovoltaic structures were recorded and a well defined response was observed in the range of absorption bands of organic dyes. The dark IN characteristics were also recorded, and electrical characterizations of the photovoltaic structures are given. The measured fourth quadrant IN characteristics under integral illumination (photoelement regime), allowed us to extract the typical photovoltaic cells parameters.

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.