| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 104 === Metal oxide nanostructure has been investigated extensively due to its wide range of physical properties; among them, zinc oxide is one of the most promising materials. It exhibits fascinating functional properties and various kinds of morphology. ZnO heterostructure especially has attracted great attention since its performance can be varied readily and further improved by combining with other materials.
The mechanism of cation exchange is remains elusive, especially in metal oxide heterostructures; it is unpredictable how the confined interface and the effects of ions diffusion will affect the transformation. In this work, the experiment was carried out in in situ UHV-TEM, which equipped with video recorder; in this way, we could observe the phenomena of the transforming directly. Moreover, we analyze the structure and composition of the epitaxial interface by Cs-corrected STEM equipped with EDS, and simulate the anion sublattice of epitaxial interface by atomic model. In this study, we deposited few nanometer of alumina onto ZnO nanowire by thermal evaporation, and successfully transformed ZnO nanowires into multiple Al2O3/ZnO heterostructure through solid state cation exchange reaction. During heating, alumina ions diffused into ZnO lattice, exchange with zinc ions, and combined with oxygen to form Al2O3 crystals mosaicked into the nanowire. In the process, the anion sublattice remains the basics of the parent crystal; therefore, it is a unique method to form new crystals with desired shape and size in nano-heterostructure.
Based on these experiment results, we infer a model of the ion path in cation exchange reactions. Additionally, the defects appeared in cation reaction were investigated, which resulted in the remaining of zinc ions.
|
|---|
