Synthesis Of Special Oxide And Nitride Nanostructures By Chemical Vapor Deposition

Due to the applications in nano-electronic, nano-photonics, etc, oxide and nitride semiconductor nanostructures (including Gallium Nitride, Tin Oxide, Indium Oxide, etc.) attracted high attention in the nanoscience research. A lot of synthesis methods, morphologies and structures about these materials have been reported.Chemical vapor deposition (CVD) is the most favorite method for synthesizing oxide and nitride semiconductor nanostructures. This method provides the morphological diversity and controllability in the synthesis of nanomaterials. In addition, it is more important that these nanomaterials have high optical and electrical quality. Different kinds of nanomaterials could be produced by changing the growth conditions, for example, 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 oxide and nitride semiconductor nanostructures through CVD, are summarized as:1. Zn-doped Gallium Nitride Nanotubes with Zigzag MorphologyWe demonstrate the synthesis of Zn-doped GaN nanotubes with zigzag morphology via a chemical vapor deposition method. Such zigzag nanotubes have single-crystalline structures, hexagonal cross-sections and wall thicknesses about 10 nm. Transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) patterns indicate that these nanotubes have alternate {0111} polar side surfaces. This zigzag morphology is a result of the building blocks alternatively growing along two equivalent directions of [1123] and [1123], which are coplanar with [0001] direction and taking it as the symmetrical line. The formation of these nanotubes is attributed to the reduction of electrostatic interaction energy caused by the {0111} polar side surfaces. These novel zigzag and tubular nanostructures would enrich the family of gallium nitride nanostructures. 2. Synthesis and Characterization of Indium Oxide Nanobubbles with Ultrathin Single Crystal ShellsWe successfully synthesized nanobubbles with ultrathin crystal shells, which are composed of nonlayered indium oxide semiconductor. Even as thin as 1 nm, only three crystal layers, the shell of the nanobubble has nearly perfect ordered atomic arrangement, exactly the same as the lattice of bulk cubic indium oxide. Different with bulk materials, these nanobubbles have flexual fringes. Normally, great strain energy is introduced by a little distortion on a nonlayered crystal compound due to shear strain between bonded layers. But this energy reduces sharply with decreasing the thickness of the crystal plate. There is no significant difference in strain energy introduced by rolling up a single atom layer of layered or nonlayered compounds. Ultrathin tubular or cage nanostructures were formed with layered materials before, but we have synthesized such ultrathin nanostructures with nonlayered material for the first time. The formation mechanism of these nanobubbles is the shell oxidation of bubbles blown by N 2 gas in catalyst droplet during the VLS growth.3. Synthesis and Characterization of Tin Oxide nanowire/nanobeltsBy decomposing GaN to get Ga, we successfully synthesized ultralong tin oxide nanowires; by the direct use of Ga, we successfully synthesized ultralong nanowires and nanobelts. Nanobelts along [011] direction were gotten, but they had unusual side surfaces. Nanobelts along [001] direction were also found, and we discussed the formation mechanism of these nanobelts which had high index side surfaces with high surface energy.