摘 要
新穎結構與新穎成分的奈米材料之開發，是一個重要的研究領域。於學術層面，新穎奈米材料提供對於材料奈米尺度孕核成長、摻混元素作用、奈米元件組裝機制的學術研究，及特殊物化特性的探討；於應用層面則提供新的形貌與性質供不同領域應用的開發。
於本論文中，我們以熱蒸鍍法為基礎，加入新的製程理念以改變奈米結構孕核與成長過程中的熱動力學，並配合基板效應於相對低溫下合成新穎的自組裝一維、二維、摻混鋁的單晶氧化鋅奈米材料，及由一維和二維奈米材料組裝的三維立體結構，並研究其微結構、成長機制、並探討在奈米光電領域的應用。
在一維度奈米材料方面，我們採用了壓力控制與反射輔助對流法合成新穎的一維奈米結構。其中氧化鋅奈米鉛筆 (nanopencil) 有進一步縮小尺寸的尖端，擁有優異的場發射性質，低起始電場與臨界電場的電子發射顯示於場發射元件的應用潛力。此外，多通道奈米電纜 (multichannel nanocable) 整合了奈米柱與六方奈米線陣列，突破傳統一維奈米材料於一端只有一個通道的單調形貌。由陰極發光光譜 (Cathedoluminescence , CL) 高強度的綠帶激光 (green emission)，暗示著結構中高濃度的氧空缺和較好的導電度，及成為奈米尺度導線並應用於傳遞多重訊號的奈米元件中的潛力。
在二維度奈米材料方面，我們藉由製程工作壓力的調整使奈米結構由線形轉變為片狀，並藉著Si基板與ZnO之間的晶格不匹配所產生的應變與晶格扭曲合成出新穎的高對稱性立體奈米材料。其中在多重對稱性奈米片整合奈米牆結構的成長過程中，我們發現罕見的應變輔助 (strain-assisted) 奈米線與奈米牆成長機制。另外，由奈米片自組裝成的角錐狀氧化鋅奈米管 (conic nanotube) 擁有低的起始電子發射電場，由Fowler–Nordheim (FN) 圖發現有別於奈米鉛筆的場發射機制。再者，本研究中合成出具有垂直奈米牆與水平奈米牆結構的氧化鋅六重對稱奈米盒。這些奈米盒是由一底層、六個垂直對稱的側壁和頂板所構成，並有單晶奈米牆磊晶成長於上。這些氧化鋅層以外觀上60或90度方向對稱建構，經由穿透式電子顯微鏡 (Transmission Electron Microscopy, TEM) 的分析，結合方式可以為雙晶或磊晶成長。這些奈米牆結構，可望成為水平與垂直奈米線的成長模版，對未來發展三維度積體奈米元件提供好的建構基礎。
在論文的第三部分，我們首次以新發展的合金氣相蒸鍍法合成出Al:ZnO奈米線與奈米管，並以穿透式電子顯微鏡之電子能量損失光譜 (Electron Energy Loss Spectrum, EELS) 技術得到鋁在奈米線中的元素分佈。有鑒於鋁的蒸氣壓低不易以一般熱蒸鍍法直接摻混，我們以合金化蒸鍍的觀念克服了此一障礙。其中Al在ZnO奈米結構中的濃度可以經由改變合金化處理的溫度而調整，在合金處理化溫度為420 ℃和500 ℃的溫度下，經由EELS三視窗技術 (three-window technique) 的分析，鋁在奈米線中的濃度可以定量求得分別為2.5和12 at.%。室溫陰極發射光譜顯示摻混Al的奈米線可發射強的UV光，且有能隙寬化的現象。
這些新穎的奈米材料，不但於場發射、多重訊號傳輸、垂直與水平奈米模版的應用上富於潛力，在合成的研究上，亦從TEM與晶體學分析發現從未報導過的一維、二維奈米材料的孕核與成長機制，經由提出理論模型解釋。

Abstract
ZnO-based nanostructures have received much attention recently due to their special optoelectrical properties. ZnO nanostructures have been synthesized and studied for the application in lasers, field emitters, nano-templates, nanosensors, nanoconductors fields so far. Above all, the continuing research and development of nanomaterials with novel structures and compositions are crucial to provide novel mechanisms for academic studies and novel properties for various applications.
In the study, we propose new concepts to fabricate a variety of ZnO-based nanomaterials by thermal evaporation. Novel one-dimensional (1D) and two- dimensional (2D) ZnO nanostructures were synthesized by the thermodynamic-kinetic transition in the nucleation and growth stages of nanomaterials along with the substrate effect. Besides, Al doped ZnO nanomaterials were synthesized by a proposed alloying-evaporation deposition. The microstructures, growth mechanisms, opto- electrical properties and potential applications of the novel nanomaterials were studied.
In respect of 1D nanostructures, a ZnO nanopencil is composed of a hexagonal nanorod on one side connected with a sharp nanoneedle on the other side. The sharp nanoneedle subtending a small angle with multiple surface perturbations is attributed for efficient field emission. ZnO multi-channel nanocables are composed of hexagonal arrays of nanowires grown on nanorods. Cathodoluminescence spectra exhibit strong green emissions, indicative of high oxygen vacancy density, which sheds a light on new applications for multi-channel nanoconductors in nanodevices.
In respect of 2D nanostructures, nanosheets instead of wire-type nanostructures were synthesized by adjusting working pressure during the nucleation and growth stages of nanomaterials. The diverse ZnO integrated nanostructures, constructed by epitaxial nanowalls and symmetric nanosheets, were synthesized via a strain-assisted self-assembled process induced by the lattice mismatch between ZnO and Si substrate. The nanowalls in the core region were formed by the interconnection of the nanowires nucleated on a rugged ZnO single-crystalline film. Beside, conic ZnO nanotubes were formed by self-assembly of numerous six-radiated branches of hexagram nanosheets. Field emission measurements show a low turn-on field emission and nonlinearity in the corresponding Flower-Nordheim (FN) plot at the lower field region. Furthermore, hexagonal ZnO nanoboxes constructed of ZnO layers with vertical and horizontal single-crystalline nanowalls were synthesized via a strain-assisted self-assembled process by thermal evaporation at a temperature of 500°C. It is shown that ZnO layers with nanowalls can be assembled at 86 and 62 to each other by twinning and epitaxy, respectively. The vertical and horizontal nanowalls have potential to be applied as templates for growth of vertically and horizontally aligned nanowires for 3D nanoelectronics.
In the third part of the thesis, Al:ZnO nanowires and nanowire/nanotube junction structures were synthesized via a proposed alloying-evaporation deposition. Al concentration in the nanostructures could be controlled by adjusting the alloying treatment in the process. Al map were first demonstrate and the Al/(Al+Zn) ratio in the nanostructures were determined to be 2.5 and 12 at.% for alloying treatment at 420℃ and 500℃, respectively, by electron energy loss spectrum (EELS). Room-temperature cathodoluminescence measurements show that the Al:ZnO nanowires exhibit a strong ultraviolet emission, which shifts to a higher energy due to Al incorporation.
The synthesized novel ZnO-based nanostructures are promising to be applied in filed emission, multi-channel nanoconductors, vertical and horizontal nano-templates for the growth of other nanomaterials etc. On the other hand, novel growth mechanisms of the nanostructures were discovered and proposed depending on the characterization with electron microscopes.

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