Synthesis, Properties and Applications of Micro/Nano Zinc Oxide Spheres

Abstract

The semiconductor material of zinc oxide (ZnO) has been studied intensively for decades due to its numerous unique electrical and optical properties, such as wide bandgap, high exciton binding energy at room temperature, and high refractive index. These properties can lead ZnO material to the applications of electronics and optoelectronics. More importantly, the realization of various kinds of ZnO micro- or nano-structures, makes ZnO capable to improve the electrical and/or optical performances of the devices. Different micro- or nano-structured ZnO has attracted much attention from researchers worldwide in the recent years as this will bright the future of ZnO in the applications of light emitting diodes (LEDs) and solar cells. And thus, developing a simple, low-cost, and environmental friendly method to grow ZnO having desired micro- or nano-structures is of great importance in the research field of ZnO material, and this becomes a key issue when a large-scale production is required in the industry. Meanwhile, the parameter control during the synthesis procedure is essential to be modified and clarified. The main focus of this thesis is on developing a simple, inexpensive, and solution based thermal method to grow spherical shaped ZnO particles having uniformly distributed size. The growth parameters for controlling the size and shape, such as the hydrate, solvent, salt concentration, reaction temperature, reaction time, seed solution, and heating rate, are experimentally studied and clarified in this thesis. This method has the advantage of large-scale production and good reproductivity with low requirements in regard to the facilities and experimental conditions in industry. At the same time, the related growth mechanism of the submicron ZnO spheres is studied, derived, and theoretically analyzed in this thesis, based on the observation in the experiments. Another focus of this thesis is on the study of the surface morphologies and optical properties of the synthesized ZnO particles. The surface morphologies are analyzed by the techniques of field emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The optical properties of the synthesized ZnO particles are experimentally investigated by Raman spectroscopy and photoluminescence at room temperature. Furthermore, the related luminescence mechanism is theoretically studied, modelled, and presented in this thesis. In order to explore the applications of the synthesized ZnO spheres, the composite of ZnO/V2O5 (zinc oxide/vanadium pentoxide) is designed, fabricated, experimentally investigated, and theoretically analyzed. The experimental results indicate that this transition metal oxide mixture can be developed to create a group of new light emission materials with high efficiency. Moreover, a silicon-based ZnO light emission device is presented in this thesis, reporting that visible light emission is observed at room temperature from the ZnO material which deposited on the hot electron emitting substrate (HEES). Finally, some of the future works of this research are suggested.