Controllable Growth And Physical Properties Of Semiconductor Nanowires And Their Arrays

Recently, one-dimensional (1D) nanostructures, such as nanotubes, nanowires, nanobelts and nanocables, have aroused intensive research interest due to their importance for fundamental studies of size-dependent physical and chemical properties and for their potential application in nanodevices. Though the research of 1D nanomaterials already has been got considerable progresses, it still remains a significant challenge to achieve controllable synthesis of 1D nanomaterials with desired morphologies, arrangement, components, structures and properties, which is a foundation and prerequisite for the applications of the nanomaterials. In this dissertation, a series of significances have been obtained on the controllable synthesis of 1D nanomaterials and relative physical properties, which can be summarized as following:1. Synthesis and photoluminescence properties of aligned silica nanowires arraysLarge area, aligned amorphous silica nanowires have been found growing on the inner wall of bubble-like silica film, which was prepared by thermal evaporation of a molten gallium-silicon alloy in a flow of ammonia. The bubble-like silica film functions as a substrate, guiding the growth of silica nanowires by a vapour-solid process. This work helps us to clearly elucidate the growth mechanism of aligned amorphous silica nanowires, ruling out the possibility of liquid gallium acting as a nucleation substrate for the growth of the aligned silica nanowires. A broad emission band from 290 to 600 run is observed in the photoluminescence (PL) spectrum of these nanowires. The emission curve could be fitted with Gauss method to seven PL peak: two blue emission peaks at 430 nm (2.88 eV) and 475 nm (2.61 eV); and five ultraviolet emission peaks at 325 run (3.82 eV), 350 nm (3.54 eV), 365 nm (3.40 eV), 385 nm (3.22 eV) and 390 nm (3.18 eV) respectively, which may be related to various oxygen defects.2. Synthesis, structure and photoluminescence properties of three-dimensional CdS nanocone arraysThe three-dimensional CdS nanocone arrays have been found growing homoepitaxially on the self-assembled Cd/CdS core-shell sphere, which was designed to serve as a template. The alternation of the wurtzite (WZ) and zinc blende (ZB) phases along the growth direction of the nanocones has been observed in the as-synthesized CdS nanocones. The WZ/ZB admixtures exhibit the features of a quantum well, which causes the two peaks centered at 503 nm (2.47 eV) and 506 nm (2.45 eV) in the room-temperature photoluminescence spectrum. 3. Aligned binary nitride nanowires grown on the Cu and Cu-based alloy wafersGaN micro/nanocone bundles with controllable size and density have been synthesized on Cu or Cu₉₅In₅ alloy wafers using a modified thermal-evaporation process. The size and density of GaN cone bundles could be efficiently controlled by adjusting growth temperatures and the components of metal substrates. The structure and morphology of the as-synthesized GaN cones were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The as-synthesized micro/nanocones are single crystals with a hexagonal wurtzitestructure, growing along the [1011] direction. The growth process follows a vapor-liquid-solidmechanism. The dependence of photoluminescence property on the size and density of GaN cone bundles at room temperature was also investigated. In addition, aligned GaN nanowires have been synthesized on a Cu wafer coated a Au film, and find that the GaN nanowires prefer to grow on the "groove" of the Cu wafer; aligned InN nanorods have been synthesized on a Cu wafer, and find the InN nanorods prefer to grow along the grain boundaries. It is believed that there have higher energy on the areas where the nanowires (nanorods) grown, which is easy for the nanowires (nanorods) nucleation and growth.4. Ga-catalysed growth and optical properties of ternary alloyed Si-ZnS nanowiresBulk-quantity ternary alloyed Si-ZnS nanowires with polycrystalline have been successfully synthesized by one-step thermal evaporation of a mixed powder of ZnS and SiO, using metallic-gallium as catalyst. The morphology and structure of the as-synthesized ternary alloyed Si-ZnS nanowires were characterized by using X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The observations reveal that the ternary alloyed Si-ZnS nanowires have the same structure with cubic ZnS or Si. X-ray energy dispersive spectrometer analysis indicates there is remarkable Si/Zn/S variation along the Si-ZnS nanowire. The room-temperature photoluminescence spectrum shows that the as-synthesized Si-ZnS nanowires have two emission peaks at 355 nm and 685 nm, and feature the superimposed optical properties of ZnS and Si.5. Synthesis, characterization and growth mechanism of core-shell nanowire heterostructuresCu-SiO₂ nanocables and ZnS-CuS core-shell nanowires have been successfully synthesized using Cu wafer as substrates:(1) Cu-SiO₂ nanocables: Cu-SiO₂ nanocables have been synthesized on the Cu wafer substrate via thermal evaporation of SiO powder, and the grown process could be described as follow: at elevated temperature, many Cu droplets were formed on the surface of the Cu wafer, and served as catalyst for the VLS growth of SiO₂ nanotubes. As the growth of the SiO₂ nanotubes, the pressure in the nanotubes would lower than that in the alumina tube, and the difference of the pressure may lead the growth of Cu-SiO₂ nanocables. It is found the CU-SiO₂ nanocables prefer to grow on the "groove" of the Cu wafer, and it is believed that there is higher energy on the areas, which is easy for the nanowires (nanorods) nucleation and growth.(2) ZnS-CuS core-shell nanowires: ZnS-CuS core-shell nanowires have been synthesized on the Cu wafer substate via thermal evaporation of ZnS powder in H₂ carrier gas, and the growth process can be described as follow: at elevated temperature, ZnS was decomposed to Zn and S vapor, and ZnS nanowires would grow on the Cu wafer in the low-temperature area by vapor-solid mechanism. And then Cu vapor was evaporated from the Cu wafer, reacted with S vapor, and form CuS. CuS covered outside of the ZnS nanowires, and the ZnS-CuS core-shell nanowires were formed at last.