具垂直方向性的氧化銦奈米線:晶向調控及光學性質研究

Abstract

本文主要探討如何利用碳熱還原法在氧化鋁基板上生長出具垂直方向性的氧化銦奈米線，並藉由環境因子的調控，成長出六角形和方形兩種截面的奈米線，其外貌形態和結晶結構可使用X光繞射儀、掃描式和穿透式電子顯微鏡三種儀器來研究，在分析後，我們發現六角形和方形截面奈米線的結晶生長方向分別為[111]和[001]，其形成原因可以兩者過飽和濃度的不同來解釋，另一方面，我們結合氣-液-固和氣-固成長力學來討論奈米線的非均勻徑長現象，這些相關生長力學的分析，在未來將有助於奈米線合成的調控能力。進一步，我們也針對六角形截面奈米線做光激發螢光光譜的探討，室溫光譜顯示奈米線在378奈米的波長有一道半高寬很窄的紫外光釋出，相對於其他文獻記載，我們的結果偏短，原因可能是低溫製程造成的低氧缺陷，另外，隨著溫度降至7K，378奈米螢光分裂成368和374奈米兩道紫外光，在長波長的波段，則產生602和648奈米兩道紅光，這四道光的成因都可歸因於氧缺陷所造成的靠近導帶或深階施子能階，進一步改良氧化銦奈米線的發光性質，未來將有助於在紫外光波段的光電應用。

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.