Structural and optical properties of ZnO nanowires synthesized by thermal vapor deposition

Abstract

To address the fascinating fundamental scientific issues and potential applications of semiconducting oxide nanostructures requires answers to two questions at the heart of condensed matter chemistry and physics research. They are why matter prefers to from nanosized wires, and what unique chemical and physical properties that nanostructures may possess which are different from that of the corresponding bulk materials. In these points, synthesizing method and structure characterization of ZnO nanowires have been investigated. In addition, the properties of the ZnO nanowires, such as optical and field emission properties have been studied in this thesis. The synthesizing method of the ZnO nanostructures using a simple thermal vapor deposition was investigated. The experimental conditions, such as reaction temperature, gas flow, source materials, substrate, and catalyst were varied to obtain various morphologies of the ZnO nanostructures. The morphologies of the ZnO nanostructures can be easily controlled by simply varying such experimental conditions. The ZnO nanonails, which consist of a hexagonal cap and a small diameter shaft, were synthesized under low reaction temperature of 450 ℃. The diameters are 100-200 nm for the cap and 50-90 nm for the shaft. The ZnO nanourchins were synthesized using $Fe(CO)_5$ catalyst which was deposited on the $SiO_2$ substrate with the subsequent hydrogen etching during 5 min at 400 ℃ under hydrogen 50 sccm and Ar 1000 sccm. The nanourchins are radially grown at the special positions of substrate. The nanourchins are starting to grow at the agglomerated catalyst particles with large size on the $SiO_2$ substrate and growing as the radial direction resulting in urchin-like morphology. When Zn powder with NiO catalyst was used as vapor source and the reaction temperature was 550-600 ℃, a large yield of the ZnO nanocombs made of ZnO nanowires can be synthesized. The nanocombs consist of a main sheet with small thickness and ...