| Summary: | 博士 === 國立臺灣大學 === 物理研究所 === 96 === The controllable vertically-aligned indium oxide nanowires with hexagonal and square cross-sections were grown on a-plane sapphire substrate by the method of carbothermal reduction. The morphologies and crystalline structures were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. After analyses, the nanowires with hexagonal cross-sections grew in [111] direction, and those with square cross-sections grew in [001] direction. The concept of supersaturation concentration is proposed to explain the formation of two kinds of vertically-aligned nanowires on the same substrate. The tapering property of nanowires is discussed by using vapor-liquid-solid and vapor-solid growth mechanisms. The growth mechanism analyses are very valuable in understanding the growth process of reagent source in the vapor route and Au catalyst, which is crucial to realize the controlled growth of vertical nanowires. Besides, the room-temperature photoluminescence spectrum of the hexagonal cross-section nanowires showed a single narrow UV emission at 378 nm, indicating the reduction of oxygen deficiencies. Furthermore, temperature-dependent photoluminescence measurement of the nanowires revealed two UV emissions (368 nm and 374 nm) and two long-wavelength emissions (602 nm and 648 nm). The near band edge emissions and deep level donors related to oxygen vacancies are proposed to explain the luminescence mechanism.
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