Morphology-Controlled Synthesis Of ZnO Crystal By A Solution-Based Chemical Route

In this thesis, a simple solution based chemical route was used to synthesize ZnO crystals aiming to control its morphologies. External conditions such as solution pH and Zn²⁺ concentration etc were investigated, and ZnO crystals were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). Based on the time-dependent experiments, the growth mechanism of ZnO crystals was discussed. These include:1. Morphology controlled synthesis of ZnO crystals: By alternating the solution pH combined with the concentration of precursors, ZnO crystals of various morphologies such as rod-like, flower-like and dumbbell-like structure, were synthesized at low temperature. Furthermore, the effects of additives such as Na⁺ and Cl^- on the morphology of the resulted ZnO crystals were also investigated.2. XRD and FE-SEM characterization of ZnO nanocrystals: The crystal structures and morphologies of ZnO samples were analyzed by XRD and FE-SEM technique. It was found that the solution pH is key important in determining the morphology of crystals architecturally. Rod-like structured ZnO crystal was found to be formed at neutral solution, whereas flower-like structured ZnO crystal was produced at higher solution pH. On the other hand, the fine structure of ZnO crystals can be further tuned by controlling the Zn²⁺ concentration.3. Growth mechanism of ZnO crystals: Time-dependent experiments were conducted to investigate the morphology evolution of ZnO crystals. It was found that different reaction intermediates were formed when different solution pH was used in growing ZnO crystal. Based on this result, different growth mechanisms of ZnO crystals in neutral and alkali solution were proposed.