Chemical Vapor Deposition Synthesis And Property Of Etal/ZnO Composite Nanostructures

Due to the wide applications in nano-photonics, nano-electronic, etc, semiconductor, metal and metal-semiconductor nanostructures attracted high attention in the nanoscience research.Among these methods, chemical vapor deposition (CVD) is the most favorite method for synthesizing nanostructures. This method provides high yield products, controllability and morphological diversity in the synthesis of nanomaterials. In addition, it is more important that these nanomaterials have high electrical and optical quality. Different kinds of nanomaterials such as nanowires, nanobelts and nanocables could be synthesized by changing the growth conditions. Furthermore, doping in the nanomaterials, heterojunction and superlattice nanomaterials could be produced by changing the gas flow rate, kinds of source materials, substrate places and temperature gradient.The main contents of my graduate thesis, focusing on the synthesis of semiconductor, metal and metal-semiconductor nanostructures through CVD, are summarized as:1. Synthesis and Electrical Property of Metal/ZnO Coaxial NanocablesAg/ZnO and Cu/ZnO coaxial nanocables were fabricated using AgNO3or copper foil as source materials. The coaxial nanocables consist of a crystalline metallic Ag or Cu core and a semiconductor ZnO shell. The diameters of the Ag/ZnO nanocables and the Ag cores could be modulated by changing Ag ratio in the source. The growth of the nanocables followed the vapor-liquid-solid (VLS) process. PL measurements show that Ag/ZnO and Cu/ZnO coaxial nanocables have the band edge emissions and the deep trap emissions due to defect states. The electrical characteristics of the Ag/ZnO contact and the influence of annealing reveal a Schottky diode behavior for a single Ag/ZnO nanocable device.The barrier height is0.313ev.2. Vapor-Phase Synthesis of Single-Crystalline Ag Nanowires and Their SERS PropertiesSingle-crystalline Ag nanowires with a face-centered cubic (fcc) structure were synthesized by a two-step vapor-liquid-solid (VLS) process. First, Ag/ZnO nanocables were synthesized in a conventional tube furnace by using AgNO3and ZnO as the source. Subsequently, Ag nanowires were successfully obtained by etching ZnO shell with3mol/L hydrochloric acid solution for120min.The diameters and lengths of the Ag nanowires are200run and tens of micrometers, respectively. The diameters of the Ag nanowires can be modulated by changing the ratio of Ag in the source. These high-quality silver nanowires were explored as extremely sensitive substrates of surface enhanced Raman scattering (SERS).3. Vapor-Phase Synthesis of Ag/ZnO NanopeapodsAg/ZnO nanopeapods were synthesized by Rayleigh instability. First, Ag/ZnO nanocables were synthesized in a conventional tube furnace by using AgNO3and ZnO as the source. Subsequently, Ag/ZnO nanopeapods were fabricated successfully by thermal annealing of Ag/ZnO nanocables. During the thermal treatment, some perturbations occurred, resulting in fragmentation of the Au core. Finally, a row of spheres was formed after prolonged annealing.The influence of annealing temperature and time was also investigated. Wire confined in nanotubes with a sufficiently large inner diameter will decay into spherical nanoparticles by gradually increased diameter undulation. Diameter undulation of wires confined in nanotubes without a sufficiently large inner diameter will be stopped by the tube shells when the undulated amplitude is equal to the inner diameter. A decay into nanorods will occur.