臺灣博碩士論文加值系統

隨著奈米碳管逐漸被應用在場發射顯示器之電子源上，如何成長高密度、規則性排列之奈米碳管陣列也成為一個重要的研究課題。在本研究中，希望透過控制多孔矽基板之結構，進一步地控制奈米碳管陣列之結構。以電化學方式成長多孔矽結構時，外加電流密度、氫氟酸溶液濃度、時間等控制參數均會影響所生成之結構，故在實驗之設計上，我們分別改變不同之實驗參數，以SEM、電阻測量等方式分析所生成之多孔矽結構，並在多孔矽基板上成長奈米碳管陣列，以了解其影響並找到最適合之製程條件。
SEM之分析結果顯示：多孔矽生成之深度與時間、氫氟酸溶液濃度及外加電流密度成正比而可達到數百m；增加電流密度使得表面孔洞密度增加，但隨著時間增加，則可能使得孔洞擴大而降低孔洞密度；增加氫氟酸溶液濃度，表面孔洞密度降低，孔洞深度增加，並在側面結構上形成較細長而分枝較多之柱狀結構；電阻值較低之矽晶圓上方能成長出柱狀之多孔矽結構，隨著電阻值之增加，多孔矽結構之連通性增加而使得側面結構破碎而散亂。
以四點探針量測電阻之變化，發現其電阻值大於105Ω-cm而無法順利量測所有的試片，也因此無法有效歸納出其與多孔矽結構之關係。由EDX之分析結果顯示，多孔矽結構中含有氧的成分，而推測由於表面積之增加，易生成二氧化矽而使得其電阻值大幅增加。
另外，在成長奈米碳管陣列上，我們在多孔矽基板上鍍厚度分別為5、10nm之催化金屬FeCo或Ni，將試片放入CVD系統中，控制氣壓為1atm，溫度自7500C到8500C，通入CH4 (10%CH4，90%Ar)以提供碳源，氣體流量為800 sccm，成長之碳管利用SEM、TEM觀察其方向性及結構，並證實了多孔矽基板之處理可幫助催化金屬均勻成核於基板上，也幫助奈米碳管陣列在試片邊緣處直立成長。

Since the carbon nanotube (CNT) arrays are widely used in field emission displays as electron sources, it is more and more important to grow high density and regularly arranged CNT arrays. In this study, we hope to control the structure of the porous silicon (PS) template so that we may control the CNT arrays structures. The current density, HF solution concentration and time are the parameters that affect the PS structure, which was prepared by electrochemical method. We changed different experimental parameters to find the optimal process conditions, and used SEM, four-point probe to analyze PS structures, and also, we grew the CNT arrays on the PS template.
The SEM pictures showed that the depth of PS increased with time, HF solution concentration, and current density. Increasing the current density caused the pore density increased, but when time was longer, the pore density would decrease and pore diameters became lager due to lateral growth of pores. Increasing HF solution concentration tended to decrease the pore density, but with deeper columnar branching structures of smaller diameters. It was also found that the columnar structures could only grow on the silicon wafers with lower resistivity. Once the resistivity was higher, the PS channels grew with more branches and the structures became broken and irregular.
The PS resistivities were measured by four-point probe. The results did not show good correlation with the PS structure and morphology. The EDX results had oxygen indication in the PS structure but not in the silicon crystal suggesting that high PS resistivities were attributed to silicon oxide (SiO2) formation.
The PS templates were deposited with 10nm nickel catalyst with e-gun evaporation, followed by a thermal chemical vapor deposition (CVD) of carbon nanotube in a furnace of 750~8500C fed with 800 sccm 10%CH4. The porous structure was apparently beneficial to the synthesis of carbon nanotube compared to the amorphous spherical carbon on non-porous silicon. In some cases, vertically aligned carbon nanotubes were observed along the edge of nickel film on porous templates.

摘要...i
Abstract...ii
圖表目錄...vii
第一章 序言...1
第二章 文獻回顧...4
2.1 I-V曲線特性...4
2.2 表面溶解反應....6
2.3 多孔矽之形成機制...8
2.3.1 The Beale model...9
2.3.2 The diffusion-limited model...10
2.3.3 The quantum model...11
2.3.4 The current burst model....12
2.4 實驗溶液之選擇...13
第三章 實驗方法...23
3.1 實驗設備....23
3.1.1 動態極化掃描...23
3.1.2 陽極處理...24
3.2 實驗步驟....25
3.2.1 動態極化掃描...25
3.2.2 陽極處理....26
3.3 實驗注意事項...27
3.4 分析多孔矽之方式...29
3.4.1 SEM分析...29
3.4.2 電阻量測...31
3.4.3 成長奈米碳管...32
第四章 實驗結果與討論...37
4.1 動態極化掃描...37
4.2 多孔矽之生成...39
4.2.1表面色澤與電壓變化...39
4.2.2 SEM觀察結果...41
4.2.3電阻之量測...46
4.2.4 奈米碳管之成長...47
第五章 結論...71
參考文獻...73

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