High-quality ZnO Nanostructures Synthesized By Vacuum Chemical Vapor Deposition

Zinc oxide (ZnO) is a typical II-VI semiconductor compound with a wide direct band gap of3.37eV and a large excitonic activation energy of60meV. ZnO has distinct physical characteristics resulting from its noncentrosymmetrical wurtzite structure, making it become a new wide band gap material after gallium nitride (GaN). Because of nanometer effect, there are apparent improvements in its mechanical, photoelectric and electric properties. For example, its outstanding field-emission, photocatalysis, absorption and bio-sensitivity characteristics.In this paper, we used a simple vacuum chemical vapor deposition method to fabricate high quality ZnO nano-structures with different morphologies, and tested and analyzed their surface morphology, crystal structure and optical characteristics by scanning electron microscope (SEM), X-ray diffraction (XRD) and photo luminescence (PL). The main content was divided into the following three parts:1. In the first part, there is a simple introduction about the physical properties and chief applications of ZnO. At the same time, we state the growth mechanism, preparation and testing methods.2. In the second part, we state the experimental process and formation mechanism In the condition without catalyzer and carrier gas, the ZnO nano-structure was fabricated by chemical vapor deposition in rough vacuum. We selected pure ZnO powder as thermal evaporation material, then the nano structures were synthesized on substrates using temperature gradient to transport the vaporized source. Meanwhile, the growth mechanism of the nanostructures were carefully discussed by means of V-S model.3. In the third part, we focused on the effect of growth conditions on ZnO nanostructures. High-quality ZnO nanostructures were synthesized by controlling growth time, growth temperature and selecting substrate material. There were different size and morphology of the synthesized ZnO nano-structures, including nanoribbon, nanoneedle and nanowire/nanorod and so on After characterizing the ZnO nanostrutures by using SEM,XRD and PL, it was found that1) the diameter of ZnO nano wires increased with increasing growth time, and along the growth direction the diameter had a trend of decreasing,while their crystal structure and optical characteristics didn’t change;2) the nanostructures fabricated on different substrates always had better crystal quality and luminescence characteristics, and there was influence of the substrates on the morphology of the nanostructures;3) different growth temperatures could result from different morphology of ZnO nanostructures, and as growth temperature decreased, the morphology of the nanostructures changed significantly.