臺灣博碩士論文加值系統

在過渡金屬材料中，鎢(W)系過渡金屬及其化合物因具有較低之電子親和能及良好的熱穩定性，故此相關材料常被應用於高溫及許多檢測儀器，如SEM、STM、TEM…等相關電子發射源領域。因此，本論文主要所成長製備之碳化鎢(WCx)與氧化鎢(WOx)奈米線材料其於場發射電子源之相關應用領域預計將具備極佳之應用潛力。
本論文旨在探討碳(C)含量改變對碳化鎢(WCx)奈米線成長特性的影響及奈米線於氣體感測器應用領域之結構設計。研究中以三個不同碳含量(重量百分比0、5、及30%)之鎢(W)及碳化鎢(WCx)靶材濺鍍沈積相關薄膜，之後，以氮氣(N2)環境下之熱處理方式於薄膜上成長高密度碳化鎢(WCx)及氧化鎢(WOx)奈米線，並於過程中調變溫度及退火時間等相關製程參數。透過SEM、TEM、SAED、XRD及XPS之分析數據發現薄膜中碳(C)原子的掺雜將影響薄膜本身之微結晶特性，且此相關特性的改變將影響奈米線的組成及成長特性。研究結果顯示，奈米線的長度將隨薄膜碳(C)含量的增加而增長，並伴隨奈米線成長密度的下降。此一現象於場發射之應用領域上，將可用以調變奈米線之成長密度、提高奈米線長度/管徑之外觀比例(aspect ratio)，以避免奈米線密度過高所引起之電場屏障效應(screen effect)。
此外，於氣體感測器應用之結構設計方面，氧化鎢(WOx)薄膜於傳統上即常應用於氣體感測器領域。而在本論文中，則嘗試以具高有效感測表面積之氧化鎢(WOx)奈米線材料作為氣體感測介質，藉由大幅增加之有效表面積，期能提高氣體感測器之特性表現。本研究中設計以濺鍍沈積之三層薄膜(W/SiO2/W)輔以蝕刻及退火製程形成奈米線橋接結構。其中，碳(W)薄膜為感測器電極，絕緣層(SiO2)厚度則決定了奈米線感測器之電極間距，如此則可不須考慮黃光微影所能達到之最小線寬即可獲得奈米線橋接所需之電極間距(0.2~0.3 μm)。由於，以此方式所製作之垂直式三層結構奈米線氣體感測器其感測特性係由氧化鎢(W18O49)奈米線本身之感測行為主導，故預期將具備優異之特性表現。

The transition metal tungsten (W) and its compounds are used in application fields of electron emission source due to their relatively low electron affinity and good thermal stability. Therefore, nano materials of tungsten carbide (WCx) and tungsten oxide (WOx) nanowires synthesized/investigated in this work are expected to be the potential candidates in future application fields of electron emitting source.
The major topics of this thesis focus on the investigation of carbon (C) content on the self-synthesis of tungsten carbide (WCx) nanowires and the structure design of tungsten oxide (WOx) nanowire gas sensors. Targets of tungsten (W) and tungsten carbide (WCx) with different carbon (C) contents (0, 5, 30 wt%) were used in this study to deposit tungsten based thin films. After that, high density tungsten carbide (WCx) and tungsten oxide (WOx) nanowires were self-synthesized on sputter-deposited films through the simple thermal annealing process under the atmosphere of N2 ambient. In experiment, the annealing temperature and duration were also modulated to investigate the growing condition of nanowires. As revealed from the results of SEM, TEM, SAED, XRD, and XPS analysis, it was found that the microstructure/crystallization of thin films would be strongly influenced by the introducing of carbon (C) atoms, and this phenomenon was observed to further affect the composition and self-growth of nanowires. Length of nanowires was seen to increase with increasing the carbon (C) content, and the growing density had a reverse situation. Experimental results of this research could be applied to modulate the growing density and aspect ratio of nanowires to avoid the screening effect in application fields of field emission.
In addition, tungsten oxide (W18O49) nanowires were also used as the sensing media to improve the sensing properties of tungsten oxide gas sensors. The enormous surface area of tungsten oxide (W18O49) nanowires was expected to increase the performance of gas sensors as compared to its bulk counterpart of tungsten oxide thin films. In this work, a triple-layer structure of W/SiO2/W films was used to vertically bridge tungsten oxide (W18O49) nanowires to fabricate gas sensors. The top and bottom layer of W films were used as electrodes and the electrode space was determined by the thickness of SiO2. The bridging space (0.2~0.3 mm) of nanowires in our study could be easily achieved without the process of conventional photolithography. Moreover, the performance of this vertical structure triple-layer (W/SiO2/W) gas sensor was expected to be drastically improved due to the sensing behavior of tungsten oxide (W18O49) nanowires.

中文摘要 I
英文摘要 III
誌謝 V
目錄 VI
表目錄 IX
圖目錄 X

第一章 序 論
1-1 前言 …………………1
1-2 奈米碳管…………………2
1-3 鎢系奈米材料…………………8
1-4 鎢系奈米材於場發射的應用 …………………9
1-5 鎢系奈米材於氣體感測器的應用…………………11
第二章 實 驗
2-1 薄膜製備…………………13
2-2 不同碳掺雜對奈米線成長特性之影響…………………14
2-3 成長碳化鎢奈米線動態行為分析…………………15
2-4 氧化鎢奈米線於氣體感測器的應用…………………16
2-4-1 薄膜製備…………………16
2-4-2 結構製程…………………17
第三章 不同碳掺雜對奈米線成長特性之影響
前言…………………19
3-1 實驗…………………21
3-2 實驗結果與討論…………………22
3-2-1 SEM分析…………………22
3-2-2 XPS分析…………………26
3-2-3 TEM分析…………………30
3-2-4 XRD分析…………………32
3-3 場發射量測…………………34
3-4 本章結論…………………36
第四章 固定退火溫度及以不同退火時間下，碳化鎢
奈米線成長過程之分析
前言…………………38
4-1 實驗…………………39
4-2 實驗結果與討論…………………40
4-2-1 XPS分析…………………40
4-2-2 SEM分析…………………41
4-2-3 TEM分析…………………46
4-2-4 XRD分析…………………48
4-3 本章結論…………………52
第五章 氧化鎢奈米線於感測器結構之應用設計
前言…………………54
5-1 三層薄膜的製備…………………56
5-1-1 薄膜參數…………………56
5-1-2 薄膜製備方式…………………56
5-2 結構製程…………………57
5-3 結構分析…………………59
5-3-1 SEM分析…………………59
5-3-2 電流-電壓量測…………………63
5-3-3 結果探討…………………66
5-4 改善方式…………………67
5-5 未來工作…………………67
第六章 總結論…………………68

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