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    Title: 氧化鋅奈米線成長機制與材料特性之研究;Growth Mechanism and Characterizations of ZnO Nanowires
    Authors: 曹福君;Fu-chun Tsao
    Contributors: 物理研究所
    Keywords: 奈米線;氧化鋅;nanowires;ZnO;CVD
    Date: 2007-06-21
    Issue Date: 2009-09-22 10:54:22 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本論文研究主題為利用化學氣相層積法,在不同條件下成長氧化鋅奈米線,並且研究成長條件對於氧化鋅奈米線的成長機制、形貌、結構及光性的影響。成長條件大致分為三個部分: 一?在不同基板上成長氧化鋅奈米線的部分,選用不同晶格常數的基板,例如:矽基板、藍寶石基板、氮化鎵基板。因為不同基板對應於氧化鋅會造成不同程度的晶格不匹配,使得氧化鋅奈米線在成長機制、形貌、結構特性及光學性質上有所影響,從實驗結果可知,在晶格不匹配程度較大的基板上(矽基板, 藍寶石基板),氧化鋅奈米線的成長機制為Volmer-Weber mode (VW mode),氧化鋅會在基板上先形成六角形島狀結構,在島狀氧化鋅的頂端形成奈米線,奈米線整體的形貌較為混亂且成長不具有特定的方向性。在結構方面具有一些缺陷的情形發生,造成光學性質上有較明顯的綠光放射。在不匹配程度較小的基板上(氮化鎵基板),氧化鋅奈米線的成長機制為Frankvan der Merwe mode (FdM mode),氧化鋅會先在基板表面形成一層薄膜,厚度約為一微米,再從薄膜上的稜角處成長出奈米線,奈米線的形貌相似且具有垂直基板表面成長的方向性。在結構上的缺陷情形不明顯,使得光學性質上只有氧化鋅能階邊緣的紫外光放射的情形。 二?成長過程中利用金作為成長反應的催化劑,使得氧化鋅的生成量也有明顯的增加,在有催化劑的情形下,氧化鋅的成長機制為固-液-氣成長機制,氧化鋅的生成量約為未使用催化劑的1000倍,但是氧化鋅的形貌非常的混亂且造成結構中有非常多的缺陷產生,使得因為缺陷造成的綠光放射的強度大於氧化鋅能階的紫外光放射。 三?不同成長時間在氮化鎵基板上可以生成不同線徑大小的氧化鋅奈米線,所有的氧化鋅奈米線皆垂直於基板表面成長,但是奈米線的長度並未明顯的增加,使得奈米線的表面與體積的比例(表面積/體積)從2.5下降到0.3,從X-ray繞射實驗中,可以觀察到當奈米線線徑越小,在奈米線成長方向上的伸展的張力越大,使得晶格常數也越大。在光學性質上,我們只觀察到氧化鋅能階邊緣的紫外光放射,這說明樣品的結構很好,但是紫外光放射的位置隨線徑變小,有一個藍移的現象發生,我們認為藍移現象是因為奈米線表面積與體積比例下降而造成的藍移現象。 In this thesis, the growth mechanism, morphology, structure, and optical properties of the ZnO nanowires grown by chemical vapor deposition (CVD) under different growth conditions were investigated with different growth condition. For ZnO nanowires grown on Si (100) and sapphire, the growth mode is Volmer-Weber mode (VW-mode) due to the large lattice misfit (>30%) between ZnO and substrate. We observed the island-like nanostructures at the bottom of the ZnO nanowires with random direction. The ZnO nanowires grown on GaN template were vertically well-aligned with 1-μm-thick wetting layer. Thus, the growth mode is attributed to the Frankvan der Merwe mode (FdM mode). The ZnO nanowires grown on the GaN template have preferred growth orientation along the c-axis. Photoluminescence (PL) spectrum exhibits only the near-band-edge (NBE) emission without defect-related deep-level emission at room temperature (RT). Characteristics of ZnO nanowires grown with and without employing Au as catalyst are studied. The density of the ZnO nanowires grown with catalyst is 1000 times than that of ZnO nanowires without catalyst. The ZnO nanowires grown with and without Au catalyst can be attributed to the vapor-liquid-solid (VLS) method and vapor-solid processes, respectively. PL spectrum of ZnO nanowires grown with Au catalyst exhibits a strong defect-related deep-level emission. It demonstrated that the ZnO nanowires grown with Au catalyst causes lots of defects in the ZnO nanowires. Size-dependent ZnO nanowires are studied. The diameter is from 37 to 250 nm. From X-ray diffraction results,there exists a tensile strain, along the c-axis, increases with decreasing the diameter of ZnO nanowires. From RT-PL spectrum, the peak of NBE emission shifts to higher energy with decreasing in the diameter of ZnO nanowires. The energy shift could be due to the surface-to-volume ratio effect with different diameter of ZnO nanowires
    Appears in Collections:[Graduate Institute of Physics] Electronic Thesis & Dissertation

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