Preparation And Properties Of ZnMgO And ZnO Nanostructures By Thermal Evaporation

Low-dimensional nanostructures are an important research field in current nano science & technology. Nanostructural ZnO materials have received broad attention due to their distinguished performance in electronics, optics and photonics, and the band-gap can be modulated by doping with Mg for further applications. Aligned ZnO nanorods have important value in filed-emission field due to the properties of negative electron affinity, high mechanical strength, chemical stability and relatively efficient low voltage phosphorescence etc.In this paper, various methods synthesizing one-dimensional pure and doped ZnO nanostructures were summarized. Based upon that, we successfully fabricated two types of ZnMgO one-dimensional nanostructures using thermal evaporation method. The growth mechanisms of the ZnMgO nanostructures were proposed, and their optical properties were investigated. We also synthesized three kinds of aligned ZnO nanorods with abrupt tips using thermal evaporation. And their field-emission properties were investigated. The main results achieved in this dissertation are given as bellow:1. Aligned ZnMgO nanorods were synthesized by thermal evaporation. The ZnMgO nanorods grew along c axis direction of wurtzite ZnO, with diameters ranging from 100 to 300 nm and 1μm lengths. The ZnMgO nanorods have single hexagonal wurtzite structure and the Mg content is 17 at%. As most ZnO nanorods, the ZnMgO nanorods have hexagonal morphology, which isn't centrosymmetric due to the doping of Mg. A 210 meV blue-shift of near-band-edge emission has been achieved at room temperature, which means the band-gap modulation effect. In particular, this preparation of ZnMgO nanorods array has good repeatability.2. Novel Aligned ZnO/hexagonal ZnMgO/cubic ZnMgO nanopagodas heterostructures were fabricated first, using a simple thermal evaporation method, through processes of low-rising-high temperature. The nanopagodas are about 600 nm at the bottom and 70 nm at the top in diameter. The molar ratio of Mg-to-Znincreases in the nanopagodas along the direction to the tip where it is 92:8, while the average is 59:41. Obvious 260 meV blueshift of the ultraviolet near-band-edge emission has been observed at room temperature. The novel heterostructures and growth mechanism have been analyzed and discussed systematically.3. Three kinds of aligned ZnO nanorods with abrupt tips were synthesized by thermal evaporation. The ZnO nanorods have single hexagonal wurtzite structure and good orientation along c axis direction. The turn-on fields of them are all bellow 0.5 V/μm, while the threshold fields are 4.5 V/um and 7 V/um respectively for the two samples with better performances. The E-J curves are well consistent with the F-N mechanism, which means that the electron emissions are field-emission. The samples with sharper tips have better field-emission property. The ZnO layer, pre-grown by PLD method, decreased the SiO₂ insulating barrier on the substrate, resulting in the improvement of the field-emission property.