Controllable Preparation And Characterization Of One-Dimensional Nano/Microstructures Of Indium Nitride

Particular interests have been arisen in InN semiconductor, owing to its superior electronic transport characteristics to other Ill-nitride semiconductors that suggests there may be distinct advantages offered by using InN in high frequency centimeter and millimeter wave devices. In addition, studies in the last few years demonstrated a band-gap energy around 0.7 eV for InN, which is much smaller than the previous reports (-1.9 eV). Thus, the band-gap energy of InN is still under debate. Furthermore, nanostructured materials are appealing and fascinating in optical, electrical and optoelectronic conversion properties, different from their bulk counterparts. Therefore, the study of one-dimensional InN nanostructures is of benefit to fundamental theoretic research and to potential device applications.The dissertation "Controllable Preparation and Characterization of One-Dimensional Nano/Microstructures of Indium Nitride" essentially involves following investigations:Firstly, wurtzite InN nanowires with uniform diameters, good crystallinity and homogeneous growth direction were synthesized by using In₂O₃ powers and NH3 as indium and nitrogen sources respectively via a conventional chemical vapor deposition process. Adjustments of reaction parameters led to the growth of nanobelts and microtubes. The as-prepared nanostructured products manifested high purity, high yield and high conversion ratio from In₂O₃ to InN. The InN microtubes are hexagonal in cross section and exhibit helical structure with both right-handed and left-handed helicities and a wide distribution of helical angles. Based on series of comparative experiments and detailed morphology imaging, the growth mechanisms of InN nanowires, nanobelts and microtubes were discussed and a unique phenomenon was revealed that InN changes from one nanostructure to another via self-evolution.Secondly, we have studied the optical, electrical and thermodynamic properties of InN nano/microstructures by using Raman, photoluminescence, optical absorption, PPMS and thermogravimetry measurements. Four characteristic modes of InN Raman scattering were observed and their temperature dependences were investigated. Fine structures in the luminescence spectra of InN nanostrutures were obtained and the emission band relating to the structures were discussed tentatively. In the optical absorption spectra, both the peak centered at about 0.2 eV and Tauc absorption edge shift systematically as the function of reaction time of the products, which is related to the composition and geometrical shape of the as-prepared products. Due to the high carrier concentration, a single InN nanowire exhibits electrical transport property characteristic of metals. TG and DSC analyses revealed that InN nanostructures began to decompose at 576°C and to be oxidized at 390°C, respectively.Thirdly, thermal oxidation of InN nano/microstructures has been performed under a low vacuum. The oxidation process of InN nanowires was investigated and InO₃/InN composite nanostructure was obtained. By the controlled oxidation treatment, InN nano/microstructures in wurtzite were converted directly into bcc In₂O₃ counterparts preserving the original geometrical shape of InN nano/microstructures, which demonstrates a novel approach to the preparation of In₂O₃ nano/microstructures with peculiar geometry.