由於石墨烯具有相當高的載子遷移率，因此被視為電子元件應用上之理想材料。近十年內，利用替代摻雜、表面轉移摻雜或光致摻雜方式造成P-型及N-型石墨烯電晶體可調控的摻雜特性也陸續被提出。然而，相對於P-型石墨烯電晶體，一個室溫下穩定的N-型石墨烯電晶體是非常難製作的。石墨烯摻雜後的電子特性很容易受環境影響，故維持石墨烯摻雜後的電子性質顯得非常重要。根據文獻顯示，當石墨烯在低氧化鈦薄膜上時被證實為擁有穩定的N型電子行為且具有高載子遷移率。為了研究低氧化鈦如何利用表面摻雜之方式，影響石墨烯的電子特性，本論文利用掃描穿隧顯微鏡與掃描穿隧能譜，直接量測石墨烯在低氧化鈦上的電子特性。此外，我們也利用狄拉克能階分佈映像圖探討在空間解析下，成長於低氧化鈦薄膜上的石墨烯如何受光照調控表面摻雜濃度之特性。在掃描穿隧能譜中，可發現石墨烯狄拉克點的能量位置低於費米能階，表示出在低氧化鈦上的石墨烯具有N型摻雜現象。實驗結果顯示出低氧化鈦上之石墨烯會受到表面載子轉移摻雜而表現出摻雜濃度增加之特性。此外，受到光致摻雜的影響，原石墨烯表面摻雜濃度較高之區域，在光照下呈現更明顯的表面載子轉移之行為。

Graphene has been considered as an ideal candidate for the applications of electronic devices due to its high carrier mobility. In the last decade, controllable doping properties of both p-type and n-type graphene-transistors have been revealed by using substitutional doping, surface transfer doping, or photo-induced modulation doping. However, comparing to p-type graphene-transistors, a stable n-type graphene transistor at room temperature is difficult to fabricate. It is very important to maintain the doping properties of graphene because the doping effects of graphene are easily influenced by the environment. According to the previous study, graphene has demonstrated a stable n-type property and high carrier mobility on a titanium suboxide (TiOx) thin film. In order to investigate the surface doping effects of the graphene, the local electronic properties of the graphene/TiOx were measured by scanning tunneling microscopy and spectroscopy(STM/STS) at a nano-scale level. Furthermore, we discuss the the concentration of photo-induced modulation doping effects at graphene thin film on TiOx with high spatial resolution by using the dirac point mapping. In the result of STS, the energetic position of the dirac point mapping is located below the Fermi level which reveals the phenomenon of N-type doping. The results show that the doping concentration at graphene/TiOx is increased by surface transfer doping. When light illuminates on the graphene surface, the degree of the dirac point shifts from the high electron doping (n+) area in graphene is more significant than that from the low electron doping (n) area. It means the photo-induced modulation doping effect brings out the significant charge transfer behavior of graphene at the region which is with high electron doping initially in dark.

致謝 i
摘要 ii
Abstract iii
目錄 iv
圖目錄 vi
表目錄 ix
第一章 緒論 1
1-1 石墨烯之特性與應用 1
1-2 石墨烯之製備法 5
1-2-1 機械剝離法 5
1-2-2 碳化矽熱裂解法 5
1-2-3 氧化還原法 6
1-2-4 化學氣相沉積法 6
1-3 石墨烯的摻雜 7
第二章 研究動機 10
第三章 實驗儀器與原理 11
3-1 掃描穿隧顯微鏡(Scanning tunneling microscopy, STM) 11
3-2 量子穿隧效應(Quantum tunneling effect) 13
3-3 穿隧電流(Tunneling current) 15
3-4 掃描穿隧能譜(Scanning tunneling spectroscopy, STS) 17
3-5 掃描模式 18
3-5-1 定電流模式 18
3-5-2 定高度模式 19
3-5-3 電流影像穿隧能譜 (Current image tunneling spectroscopy, CITS) 20
3-6 掃描探針製備 21
3-7 超高真空系統 23
3-7-1 真空計 23
3-7-2 真空幫浦 25
第四章 實驗結果與討論 28
4-1 樣品資訊 28
4-2 石墨烯之形貌分析 29
4-3 掃描穿隧能譜的狄拉克點(Dirac point)位置之分析與討論 31
4-4 低氧化鈦對石墨烯之表面轉移摻雜現象 34
4-5 雷射光照射對石墨烯之光致摻雜現象 36
4-5-1 石墨烯之光致摻雜現象之剖面觀察結果 38
4-5-2 石墨烯之光致摻雜現象之空間解析及狄拉克點映像分析(Dirac point mapping) 39
4-5-3 石墨烯之光致摻雜現象與表面波紋(Corrugation)結構的關係 41
第五章 結論 43
參考文獻 44

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