Synthesis And Characterization Of Oxide Composite Nanostructures

ZnO, SnO₂ and In₂O₃ are important semiconducting oxide, which have demonstrated great potential applications in optical and electrical devices. Their composite materials, such as ZnO/SnO₂ and ZnO/In₂O₃ composite also possess superior physical/chemical properties. The research on these nanostructures have become a challengeous research focus in recent years.In this thesis, ZnO/In₂O₃ and ZnO/SnO₂ nanocomposites have been successfully synthesized by means of thermal co-evaporation from mixture sources of ZnO/In₂O₃ and ZnO/SnO₂ powders. Their crystalline structures, morphologies, chemical compositions, photoluminescence properties were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and combined micro-Raman/fluorescence spectroscopy. Based on the analysis of the experiment results, growth mechanisms of nanostructures were further discussed. The major results of the experiments in this paper are described as follows.1) ZnO/In₂O₃ composite oxide nanorings were synthesized by thermal co-evaporation from mixture sources of ZnO/In₂O₃ powder, with Al₂O₃ and Si 111 used as substrates. According to TEM images, there are 2 types of nanorings in the sample. In the nanoring of type I, the top and the bottom surfaces were polar surfaces. In the nanorings of type II, the inside and the outside surfaces were polar surfaces. Nanorings were grown by VS mechanism. At high temperature, ZnO and In₂O₃ were evaporated and became Zn, In and O2 vapor. Transferred to relatively low temperature area, vapor phase deposited and were oxidized. Nanobelts with polar surfaces as side surfaces were formed at first. Then, as nanobelts got longer, they tended to coil and form a loop. The different ways nanobelts coiled leads to different types of nanorings. The photoluminescence (PL) spectra recorded from ZnO/ In₂O₃ nanocomposite show only a strong peak corresponding to UV emission of ZnO at about 373-380 nm, without any peak in the visible region.2 ) Nanocombs, nanowire and nanocables were successfully synthesized by thermal co-evaporation from mixture sources of ZnO/SnO₂ powder, with Al₂O₃ used as substrates. The morphology of nanostructure was determined by the molar ratio of ZnO/SnO₂ source. The growth mechanisms of nanostructures were different. Nanocombs and nanowires were grown by VLS process, when nanocables were grown by Vapor-Solid process. Based on the analysis of EDS, Raman and TEM results, it was found that nanocables were consisted of ZnO core and Zn₂SnO₄ sheath. The ZnO core of nanocables grew along the direction of 0001 . The expitaxial relationship between ZnO and Zn₂SnO₄ were Zn₂SnO₄ 110 || ZnO 1210 ,Zn₂SnO₄ 111 || ZnO 0001 . The PL spectra recorded from ZnO/SnO₂ nanowires show a strong UV peak (380.732 nm) and a strong emission in the visible region. And the PL spectra recorded from nanocables showed only one strong peak corresponding to UV emission of ZnO at about 380.58 nm, indicating that the sheath of Zn₂SnO₄ prevented the oxygen deficiency in the surface of nanocables.