Hrytsak L. Synthesis and characterization of materials with different dimensionality based on zinc oxide

The dissertation is devoted to the purposeful modification of the optical-spectral, electric, heat conductivity and photocatalytic properties of zinc oxide by means of lowering of system dimensionality and changes of the technological processes in order to obtain the effective multifunctional materials for the optoelectronics. The investigations of the electrical and thermal conductive properties of composites based on nano- and micropowders of zinc oxide established that growth of the thermal conductivity of the the nanocomposites of ZnO in comparison with the microcomposites was caused by ballistic thermal conductivity, increasing of the exciton thermal conductivity and a decreasing of the contact thermal resistance. The low temperature photoluminescence spectra of ZnO nanostructures grown by hydrothermal method were investigated. There were observed and interpreted the two distinct peaks: more intensive one with a maximum at 3,36 eV and less intensive at 3,32 eV. Study of the thermally stimulated luminescence (TSL) of ZnO nanostructures grown from a vapor phase on a sapphire substrate provided information about the nature of their green emission band. The parameters of the adhesion centers are determined: the trap ionization energy, the trap carrier trapping cross section and the frequency factor. The investigations of ZnO nanostructures luminescence are important for creating of the effective LEDs and lasers based on them. The effect of ion etching on the photocatalytic properties of zinc oxide nanostructures grown from a vapor phase and by the hydrothermal methods have been investigated. It was found that zinc vacancies were predominant for ZnO nanorods grown from a vapor phase, whereas for ZnO nanorods grown by hydrothermal method ‒ a high concentration of hydroxyl group plays the most important role. A significant effect of the dye decomposition rate increasing under the action of an electric field has been found, which was associated with a more efficient charge redistribution and more high hydroxyl radicals’ concentration on the catalyst surface. The fractal analysis of the surface of the synthesized nano- and microstructures of zinc oxide was performed. The technology of producing of the nanocomposite photocatalysts based on zinc oxide and porous silicon (ZnO/p-Si) have been developed. ZnO nanowires are characterized by a more developed surface in comparison with the films composed of the vertically oriented zinc oxide nanorods. The technology of production of the nanocomposite photocatalysts based on zinc oxide nanoparticles and graphene oxide bilayer (ZnO/rGO) have been developed. The absorption of reduced graphene oxide in the visible spectral range was estimated and the minimal electron transition energy was determined. The catalytic properties of the nanocomposite in the degradation of methyl orange were investigated and the comparative analysis of bilayer rGO and ZnO nanostructures was carried out.