Zinc Oxide and Vanadium Pentoxide Nanostructures and Their Photonic and Intercalation Properties

Abstract

V2O5 and ZnO nanostructures have vast applications in the emerging technologies. The purpose of this study is to produce V2O5 and ZnO nanostructures and explore their properties with a special emphasis on optical and intercalation properties. The study of formation mechanisms, nanostructure and properties of ZnO and V2O5 will be important for their electrical, optical, photonic and chemical applications. ZnO thin films are prepared on glass by oblique angle deposition (OAD) technique via magnetron sputtering. The vapour flux angle α is varied from 40° to 80°. The influencing factors including pressure, deposition current and deposition angle on the microstructure and density of the films are investigated. The slanted columns of ZnO grains grow at an angle less than α and form porous films. It was also found that ZnO grains consisted of small crystals; grow one on top of the other with the crystal orientation not along the grain growth but perpendicular to the substrate. Optical properties of the films were investigated by UV-Vis spectrophotometer. The average transmission of light in the visible region is in the range of 76 – 97%. V2O5 films are prepared on various substrates by magnetron sputtering, followed by heat treatment in oxygen. It is found that the annealing temperature, the thickness of the film and the substrate greatly influence the phase, crystallinity and microstructure of the films. Rietvel fitting of the XRD patterns shows metastable beta V2O5 crystal structure on glass substrate after annealing, while beta coexisting with alpha V2O5 phase formed on F:SnO2 coated glass substrate. The silicon substrate favours only alpha phase. Moreover, crystal symmetry of V2O5 film gets higher from beta monoclinic to tetragonal with increasing film thickness. Optical properties of the films were investigated by UV-Vis spectrophotometer, giving an indirect bandgap of 2.2 eV for the pre-heated films which was reduced to 1.35 eV after annealed at 500°C. Multi-oxide systems have improved physical and chemical properties. ZnO – V2O5 binary system is deposited on glass and silicon substrates by using techniques of bilayer, multilayer and dual sputtered magnetron sputtering followed by heat treatment. Phases containing ZnO, V2O5, Zn2V2O7, Zn3(VO4)2 and lower vanadium oxides were formed depending upon the ZnO and V2O5 atomic ratio, annealing temperature and substrate. Photoluminescence of the films were studied by a He-Cd laser, indicating that the annealed samples containing stoichiometric α-Zn3(VO4)2 exhibited strong light emission in the visible region of ~ 528 nm. Vandate groups VO4 -3 were considered luminescent centres for light emission. Insoluble V2O5/tetra-n-butyl titanate (TBO) hybrid xerogel is prepared by the sol-gel method. This novel material has proved to be an efficient absorbent for Rhodamine B (RhB) dye in water due to its unique layered structure, which can accommodates RhB molecules between its interlayers. Processing parameters of V2O5/TBO xerogel were studied in relation to the RhB absorption property, indicating that short time ultrasonication of V2O5 xerogel in concentrated TBO/ethanol solution substantially increased the absorption capacity. The amount of RhB absorbed per unit mass of xerogel is comparable to the absorption capacity of activated carbon. Analyses demonstrated that the absorption of RhB occurred in the interlayer spacing of the xerogel. This study may develop a novel absorbent for the removal of dyes from waste water.