Nanostructures And Microstructures: Synthesis, Structure And Optical Properties

In this thesis, various nanostructures have been synthesized using templates made from gas-phase deposition by a two-step thermal evaporation method, including quasi one dimensional ZnO nanowires grown on the ZnO buffers that cover the Zn microspheres, nanowire-tipped ZnO nanocone arrays on two dimensional Zn2SnO4 base and cracked hollow amorphous silica microspheres synthesized with metallic Zn microspheres as templates. The two-step thermal evaporation method means that, first step, the synthesis of different kinds of templates at relative low temperature and corresponding structures based on these templates were made at higher temperature as second step. We proposed the growth mechanism and optical property of these structures after the characterization of products such as morphologies, composition, crystal structures and fluorescence properties. The following is the main contents of our research.1. The growth mechanism and luminescence property of urchin-like ZnO nanostructures synthesized by two-step thermal evaporationFirst step, in the pure Ar protective atmosphere, the Zn powder was evaporated and deposited downstream to synthesize Zn microspheres. Second step, the mixed powder of ZnO and graphite was react at high temperature and deposited on the Zn microspheres to form ZnO buffers for further growth of ZnO nanowires. After characterization of products, the result consist with expectation, the nanostructures are structures that have Zn cores and ZnO nanowires radially grown on the ZnO buffers on the surface of cores. The diameters of spheres and nanowires are 1-5μm and 80 nm, respectively. We found there were many particles whose diameter is about 210 nm on the Si substrate where less nanostructures were synthesized, which affects the optical property as the results of Gauss fit have exhibited that the ultraviolet emission (396 nm) shift to the violet emission (401 nm) in the product which contains these particles.2. Nanowire-tipped ZnO nanocone arrays on Zn2SnO4 base synthesized via two-step thermal evaporation: growth mechanism and optical propertyFirst step, Zn templates were synthesize as the Zn powder was evaporated and deposited downstream at a relative low temperature (500℃) in the pure Ar protective atmosphere. Second step, at high temperature (1100℃), the mixed powder of SnO and graphite was evaporated and deposited on the Si substrate to synthesize Zn2SnO4 base and ZnO nanocones. The nanocones are nanowire-tipped and have a symmetry morphology about the growth direction [10-10]. Based on the calculation of the lattice mismatch of different families of crystal planes in ZnO and Zn2SnO4, the orientation relationship between nanocone and base was illustrated and a model of lattice matching was built to propose a possible growth mechanism of ZnO nanocones. In the study of fluorescence property of product, we found the emission peaks come from the ZnO nanocones and Zn2SnO4 base, the peak at 490 nm is attributed to the oxygen vacancy in Zn2SnO4 base, which is a cause of broadening of green emission peak. Meanwhile, a atom migration model was built to explain various defects that contribute to the Gauss peaks.3. The cracked hollow SixO spheres synthesized by a two-step thermal evaporation approach: growth and cracking mechanism and optical property Zn microspheres were made at low temperature in the first step and mixed powder of SiO and graphite was react at high temperature for 1 h to deposit Si on the Zn microspheres when the Zn melt and the Zn gas broke through the silicon shell, a small quantity of Zn and ZnO retained at the breach of hollow silica spheres and oxidized by the oxygen in the Ar+10% O2 , which was demonstrate by the analysis on the XRD and EDS spectra. Finally, the clapyron equation and the vertical and horizontal deposition model were built to illustrate the cracking mechanism.