臺灣博碩士論文加值系統

本研究旨在探討一維和多維氧化鋅奈米線的成長機制與單根奈米線上的聲子侷限效應。氧化鋅奈米線係利用鈦輔助化學氣相沉積法製作，成長溫度範圍在攝氏四百度到七百度之間。氧化鋅奈米線的尺度與維度可經由改變退火溫度而調控之。氧化鋅奈米線平均直徑為33.2奈米至191.5奈米，其平均值隨退火溫度增加而上升。在退火溫度攝氏五百度以下，只能在樣品表面上發現一維氧化鋅奈米結構；而高於攝氏五百度，則有三維奈米線成長其上。晶格結構分析結果顯示，氧化鋅奈米線為烏綵六方晶系結構，空間群為P63mc，成長方向為[110]。氧化鋅奈米線的成長機制可歸因於短程擴散機制。鋅原子在氧化鋅薄膜的擴散情形可用二維能量分佈光譜技術描繪。擴散模型則用於計算不同樣品間的擴散活化能值，結果顯示活化能值約介於晶格擴散活化能值的0.26至0.35倍，顯示氧化鋅奈米線成長係藉由晶粒邊界、錯位和缺陷等短程擴散路徑。單根氧化鋅奈米線的拉曼光譜可藉由共軛聚焦拉曼光譜儀沿著成長方向逐點掃描，而拉曼譜線可由Viogt方程式擬合。與缺陷相關的E1-LO模的出現證實奈米線底部存在混合態。繞射峰的紅移可歸因於聲子侷限效應，而藍移則歸因於鋅氧缺陷態、尺度效應與應力效應。聲子侷限模型則用來探測不同位置的相關長度。藉由擬合E2H模的譜線，以計算奈米線上不同位置的缺陷平均距離，擬合結果顯示在高溫下成長的樣品具有較佳的結晶性。

The growth mechanism and the phonon confinement effect in one-dimensional and multi-dimensional ZnO nanowires are investigated. The ZnO nanowires were fabricated by a Ti-assisted chemical vapor deposition method without any catalyst in a temperature range of 400-700 ℃. The mean diameter ranging from 33.2 to 191.5 nm increased with the increasing temperature. The dimensionality can be controlled by adjusting the annealing temperatures. Below 500 ℃, only one-dimensional ZnO nanowires can be found on the sample surface, and, above it, three-dimensional ZnO nanowires were able to be grown. ZnO nanowires have a hexagonal structure with a space group of P63mc and the [110] growth direction. The formation of ZnO nanowires was attributed to the short-circuit diffusion. Energy dispersive x-ray spectroscopic mapping technique was used to depict the diffusion of zinc atoms through ZnOx film from the zinc base to the film surface. A diffusion model was utilized to calculate the activation energy of the diffusion for various samples. The result shows that the activation energy is 0.26-0.35 times the activation energy of ZnO lattice diffusion, revealing that the growth of ZnO nanowires was related to the diffusion goes through the grain boundaries or sub-boundaries and then forms ZnO nanowires. The Raman spectra along the growth direction of a single ZnO nanowire have been characterized by Confocal Raman spectroscopy. The Raman intensity can be described by a multi-voigt function. The appearance of a defective state of the E1-LO mode proved a mixed state in the bottom region of the ZnO nanowires. The downshift of the Raman scattering peak can be interpreted by the phonon confinement effect while the upshift can be attributed to zinc interstitials, oxygen vacancies, the size effect and the strain effect. A phonon confinement model was utilized to obtain the correlation length by fitting the Raman curves of the E2H mode in various positions. The result shows that ZnO nanowires fabricated at high temperatures have a high crystallinity.

誌謝 i
摘要 ii
Abstract iii
Contents v
List of figures vi
List of tables x
Chapter 1 Introduction 1
1-1 Background and motivation 1
1-2 Short-circuit diffusion 5
1-3 Theory of phonon confinement 9
1-4 Properties of ZnO 12
Chapter 2 Synthesis and Experiments 19
2-1 Synthesis methods 19
2-2 Experiments 21
2-3 Measurement instruments 25
2-3-1 Field-emission scanning electron microscopy 25
2-3-2 Energy dispersive X-ray spectroscopy 26
2-3-3 Transmission electron microscopy 28
2-3-4 Confocal Raman spectroscopy 29
Chapter 3 Growth mechanism 35
3-1 Morphology analysis of ZnO nanowires 35
3-2 Crystal structure analysis of ZnO nanowires 40
3-3 EDS Line scan 47
3-4 Two dimensional EDS mapping 57
Chapter 4 Phonon confinement effect 71
4-1 Raman mapping 71
4-2 Analysis of the E2 mode 84
4-3 Correlation length 90
Chapter 5 Conclusions 99

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