Synthesis And Characterization Of Zinc Oxide And Bismuth Oxide Nanowires Grown By Magnetron Sputtering

Author : Ruiqun Chen
Publisher :
ISBN 13 :
Total Pages : 388 pages
Book Rating : 4.:/5 (77 download)

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Download or read book Synthesis of Zinc Oxide Nanostructures by Wet Oxidation Process written by Ruiqun Chen and published by . This book was released on 2011 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: The studies on zinc oxide (ZnO) nanostructures have been intensified worldwide in the last decade. This is because ZnO as a semiconductor material has some unique properties, such as a wideband gap of 3.37 eV and high exciton energy of 60 meV at room temperature. This makes ZnO a potential and low cost substitute for GaN for blue to ultra-violet (UV) light emitting applications. Furthermore, it is known that ZnO material can easily form various nanostructures such as nanowires and nanobelt, which have the potential for catalysis or solar cell applications due to their high specific surface area and reactivity. Up to now, a large range of ZnO novel nanostructures has been synthesized by different groups with different methods. However, most of the current used techniques either has problems regarding to the requirements for high temperature and/or vacuum conditions incorporating the necessity of using expensive equipments, or difficulties with quality control and pollution. The focus of this thesis research is on the development of an alternative way of producing high quality ZnO nanostructures at moderate temperatures with low requirements in regard to facilities and experimental conditions. The method is wet oxidation, where Zn precursor is prepared by magnetron sputtering and oxidation of the Zn precursor films in wet O2 to produce ZnO nanostructures. In this thesis, various experimental factors were studied for their impacts on the formation of ZnO nanostructures. The growth mechanism of the ZnO nanostructures was then derived and checked with the experimental results. The structural and optical properties of the ZnO nanostructures were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), cathodoluminescence (CL) and photoluminescence (PL) measurements to gain the understanding of the growth process in wet oxidation. The doping methods for the wet-oxidation technique have been developed in two ways. Ag doping was achieved by mixing small amount of Ag into Zn precursor in advance of wet oxidation; and during the wet oxidation, the Ag atom would diffuse into the ZnO nanostructures to form Ag doping. Ag doping was confirmed by SEM, TEM, X-ray photoelectron spectroscopy (XPS) and PL. However, TEM observation showed that Ag doping was non-uniform in the ZnO nanowires, with a concentration gradient along the nanowire growth direction. XPS results demonstrated that the doped Ag existed in 1+ and 2+ chemical states, rather than in the metallic element state. PL spectra indicated that Ag doped ZnO nanowires had better light emission than the un-doped ZnO. N doping was conducted by introducing NH3 into the wet oxidation atmosphere, so that Zn could react with NH3 at the same time as being oxidized. SEM studies demonstrated that the nanowires grew better from Ag-Zn precursor films than from Zn precursor films with the same oxidation conditions. The presence of Ag reduced the temperature required for the Zn-NH3 reaction to take place. This resulted in the amount of Zn2N3 crystals being so large that it could be observed under TEM. The Zn2N3 crystals would transform to ZnO during the oxidation process with certain amount of N atoms remaining in the crystal lattice: this was confirmed by XPS measurement. Wet oxidation can also be used to produce ZnO and ZnO/TiO2 porous films. The porous structure was formed by reactive sputtering and preserved during wet oxidation. TiO2 nano-clusters in anatase phase were formed on the surface of the ZnO/TiO2 porous film after the wet oxidation, and the porous ZnO/TiO2 film showed enhanced PL spectrum in visible light range. The enhanced PL emission is believed to come from TiO2 due to its resonant effect with ZnO. Due to the large surface area resulted from the high porosity, ZnO and ZnO/TiO2 films have shown great photocatalysis activity for degradation of organic compounds. The ZnO/TiO2 porous film showed a better performance under visible light than the ZnO porous film, and more than 70% of the estrone could be degraded within 4 hr under visible light irradiation, with ZnO/TiO2 porous film as the catalyst. A further increase of TiO2 content in the porous film using the sol-gel method can increase the degradation percentage to more than 80% within the same time period. These tests demonstrated that these porous films would have great potential in the photocatalysis application. Some directions of future development for this research are suggested in the last part of this thesis.