Abstract
Semiconductor nanowires and nanorods are ideally suited to be the important building block for interconnects of transistors, junctions of metal-semiconductors and the tips of emitters. In this thesis, we demonstrate the synthesis of ZnO nanowires by thermal vapor transport and the characterization of the wires.We first present the area-selected synthesis of ZnO nanowires by low-temperature (500□C) vapor-liquid-solid (VLS) approach. The growth of the nanowires was controlled by Au catalyst and water vapor, as an oxidizing agent, is helpful to the growth of the ZnO nanowires. High-resolution transmission electron microscopy studies demonstrate that the nanowire is single crystal and room-temperature photoluminescence show that the ZnO nanowires are of good optical quality.We then present another way to grow ZnO nanowires. We grew uniform hexagonal prismatic zinc oxide rods all over the entire alumina substrates at 550□C by a two-step oxygen injection process, no matter whether the substrates were coated with catalyst or not. We also studied the influence of atmosphere and temperature, and proposed the growth mechanism was self-catalyzed VLS process and vapor deposition growth.By using two-step oxygen injection process, we got the epitaxial needle-like ZnO nanowires grown vertically over entire epi-GaN/sapphire substrate at 550□C without employing any metal catalysts. The two-step oxygen injection strategy is the key of successful synthesis. Because it could deposit a thin zinc film in the first step, and the zinc layer not only prevents the GaN layer from contacting with oxygen molecules directly to form Ga2O3 phase, but also forms ZnO nucleus seeding layer.Finally, We also grew needle-like ZnO nanowires vertically over the entire Ga-doped conductive ZnO film at 550□C. The nanowires were grown preferentially in the c-axis direction on the ZnO film. High-resolution transmission electron microscopy was used to confirm that the nanowires are single crystal. Furthermore, we used the nanoneedles as the tips of emitters and got the turn-on field of field electron emission to be about 18 V/□m at current density of 0.01 □A/cm2.