| This thesis concentrates on developing novel methods to synthesize one-dimensional nanostructures in a controlled manner and studying of their applications such as field effect transistors. Chemical Vapor Deposition and Pulsed Laser Deposition were used as the main techniques. The target materials include semiconductors, transition metal oxides and single-walled carbon nanotubes.;Horizontal tube furnaces were used to grow single crystal Gallium Nitride and Indium Nitride nanowires. The growth followed vapor-liquid-solid mechanism. By controlling the catalyst size, location and density, we were able to gain the control of the nanowire diameter, location, density and orientation for the first time. The control is very important for their application as optoelectronic devices. Transistors made of GaN and InN nanowires were characterized at different temperatures and their applications as polarized ultraviolet light sensors were demonstrated. Pulsed-laser-deposition method was applied to synthesize transition metal oxide nanowires. MgO nanowires were grown first as templates by CVD method. YBCO, LCMO, PZT, Fe3O4 were deposited on the nanowire templates uniformly by PLD to form core-shell nanowire structures and their compositions were preserved. This method can supply a group of previously unavailable materials to the nanotechnology community and opened up a lot of potential applications. Devices made of transition metal oxide nanowires offer enormous opportunities to explore intriguing physics at the nanoscale dimensions such as magnetoresistance at room temperature.;Finally, highly aligned SWNT arrays were synthesized on a-plane and r-plane sapphire. It was found that the nanotubes were aligned normal to the [0001] direction for growth on the a-plane sapphire. In contrast, no orientation was achieved for growth on the c-plane and m-plane sapphire, or when Fe films, instead of ferritin, were used as the catalyst. Such orientation control was related to the interaction between carbon nanotubes and the sapphire substrate, which is supported by the observation that when a second layer of nanotubes was grown, they followed the gas flow direction. These aligned nanotube arrays enabled the construction of integrable and scalable nanotube devices---top gated transistors and nanotube FETs on flexible substrates. |
