成長單一方向氧化鋅奈米線及其光學、場發射、電子傳輸與光催化特性之分析

Abstract

本研究以碳熱還原法結合VLS機制，成功地(100)面矽基板上成長單一方向的氧化鋅奈米線奈米陣列，藉控制不同基板溫度、氧氣流量和爐管內總壓可得到各種形貌的氧化鋅奈米線。在基板溫度為750 ℃，通以氧氣10 sccm，控制壓力0.75 torr的條件下，可得長寬比達250，結晶性良好、成長方向為[0001]的一維氧化鋅奈米線。在螢光光譜儀量測下，可觀察氧化鋅奈米線發光主要來自兩個波長：386 nm和506 nm，且506 nm相對於380 nm的發光強度會隨著氧流量增加而下降；當氧流量固定時，則以奈米線表面積決定強度，表面積增加，強度增強。在場發射特性的量測上，本研究所成長的單一方向氧化鋅奈米線陣列皆具有良好的場發射特性，尤其是類似鉛筆狀的奈米線，其獨特的結構使之具有低的起始電場約3.82 V/μm與高的電場增強因子約2303。除此之外，以傳統的電子束微影製作單根氧化鋅奈米線的場效電晶體，可觀察其為一種N型半導體的特性，並利用閘極電壓可有效控制電流的大小。最後，在氧化鋅奈米線的光催化實驗中，顯示氧化鋅奈米線為一種良好的光觸媒材料，且其催化效率與表面積相關，較細的奈米線擁有較好的催化效果，並進一步利用蒸鍍金薄膜，藉由退火而在奈米線上形成金粒子，使其減少光電子-電洞對之結合，且尺寸越小的金粒子提升催化速率越明顯，在未來則可運用於環境保護，作為分解有機汙染物的催化劑。

In this study, we have successfully synthesized well-aligned ZnO nanowires (NWs) on Si(100) by using the process of carbothermal reduction and vapor-liquid-solid method. Scanning electron microscopy and transmission electron microscopy results confirm that ZnO NWs exhibit nearly perfect single crystal of wurtzite structure and grow along [0001] direction. The influences of substrate temperature, total pressure and oxygen partial pressure on the growth were discussed. Room temperature photoluminescence spectra of as-prepared ZnO NWs were recorded, which reveals a strong UV emission and a broad green emission. The green emission was resulted from oxygen vacancies, and the intensity increased as the decrease of partial oxygen pressure and the chamber pressure as well as the increase of ZnO NWs surface ratio. The well-aligned ZnO NWs show good field emission properties, and the constructed emitter of pencil-like ZnO NWs exhibit low turn-on field (3.82 V/μm) and high field enhancement factor(β= 2303). The electrical transport properties of a single ZnO NW field-effect transistors (FETs) prepared by the electron-beam lithography with a back-gate structure were investigated. The device exhibited the N-type semiconductor character, and the drain current can be controlled by changing gate voltage. Finally, we showed that as-prepared ZnO NWs with small diameter on substrate have good photocatalytic activity toward degradation of MB. We also added Au nanoparticles on the surface of ZnO NWs using e-gun deposition and annealing. The smaller Au nanoparticles decreased the recombination rate of hole-electron pair due to the greater of Fermi level shift to conduction band. Hence, adding Au nanoparticles that was a promising method to enhance the photocatalytic activity of ZnO NWs. It is significant that photocatalyst fabricated by ZnO NWs can apply to the degradation of organic pollution, and solved the environmental problems.