臺灣博碩士論文加值系統

本實驗利用兩階段氣相傳輸法成功合成出SnO2/Graphene多階層奈米異質結構。我們探討了不同成長時間對於石墨烯成長的影響，也利用石墨烯在不同成長時間下的形貌變化探討其成長機制。實驗結果顯示，在1000˚C通入90:30的甲烷與氫氣混和氣體，隨著成長時間的增長，石墨烯的層數會隨之增加，而且成長機制和一般低壓化學氣相沉積(APCVD)有所不同，在這裡C-Cu合金顆粒在成長中扮演著提供碳源讓石墨烯成長的重要角色，甲烷在高溫分解為游離碳物種，此時會在石墨烯上成長出初始的石墨烯晶粒，而在石墨烯晶粒的周圍會因為碳物種的吸附而形成C-Cu合金，C-Cu合金提供了石墨烯足夠的碳源讓石墨烯繼續成長。石墨烯上成長SnO2奈米線是先在石墨烯上鍍金，利用金觸媒輔助的VLS的成長機制，合成出正方晶系(Tetragonal)金紅石(rutile)結構的SnO2奈米線，成長方向為[021]。在氣體感測方面，將石墨烯及SnO2/Graphene多階層奈米異質結構分別製成感測元件並在不同溫度不同濃度的NO2氣體進行感測特性量測。結果顯示，SnO2/Graphene多階層奈米異質結構比單純石墨烯擁有更高的靈敏度，這是因為此種多階層奈米異質結構擁有較大的比表面積，且SnO2奈米線和石墨烯接點產生蕭特基能障進而有利於捕捉電子，因此表現出較高的靈敏度。

In this study, SnO2/Graphene hierarchical nanostructures had been synthesized successfully by a two-step vapor transport method. We not only explore the effects of the different growth time on the resultant structures of graphene, but also observe the morphological evolution to investigate the growth mechanism. The results show that the number of the layers of graphene increased with increasing the growth time when a mixture of methane and nitrogen with a ratio of 90:30 was introduced and the growth temperature was kept at 1000˚C. Moreover, we found that the growth mechanism of grapheme grown on the copper foil in this study is different from that grown by the low pressure chemical vapor deposition (APCVD). Here the granules of C-Cu alloy play an essential role in the growth process of Graphene. When methane is disassociated into ionization species, small graphene grain will grow on the surface of copper foil in the initial stage. The absorption of carbon atoms around the graphene grains will lead to formation of C-Cu alloy that can provide sufficient carbon atom sources for the continuous growth of graphene. For the growth of SnO2 nanowires on the graphene substrate, a thin layer of gold was deposited on the graphene substrate and SnO2 nanowires were grown by an Au-catalytic VLS growth mechanism. The structure of SnO2 nanowires is confirmed to be tetragonal rutile and the growth direction is along [021]. For gas sensing measurements, sensors based on graphene and SnO2/Graphene hierarchical nanostructures are fabricated and their sensing properties to NO2 gas with various concentrations were measured at different operation temperatures. The results show that the SnO2/Graphene hierarchical nanostructures have higher sensitivities than graphene, which can be attributed to their high surface-to-volume ratios, and the formation of numerous Schottky barriers between SnO2 and Graphene that provides the advantage of catching electrons.

摘要......................................................i
Abstract.................................................ii
目次.....................................................iii
圖目次.....................................................v
表目次....................................................vi

第一章 緒論..............................................1

第二章 文獻回顧...........................................2
2-1 半導體氣體感測器之應用....................................2
2-2 半導體氣體感測器發展及其遭遇問題............................5
2-3 石墨烯簡介..............................................7
2-3-1 石墨烯的合成......................................7
2-3-2 石墨烯氣體感測之應用...............................12
2-4 多階層奈米結構在氣體感測器上的發展..........................15
2-5 研究動機與目的..........................................17

第三章 實驗方法與步驟........................................18
3-1 實驗設計與流程..........................................18
3-2 銅箔的準備與前處理.......................................19
3-3 石墨烯的合成............................................20
3-4 石墨稀的轉印............................................21
3-5奈米線的成長......................................21
3-6 氣體感測元件的製作與量測..................................23

第四章 結果與討論............................................24
4-1 石墨烯之合成.....................................24
4-2 石墨烯之拉曼圖譜分析..............................25
4-3 石墨烯的成長機制..................................28
4-4 SnO2/Graphene多階層奈米異質結構的合成及其晶體結構分析........................................................30
4-5 氣體感測特性量測..................................33
第五章 結論................................................38
參考文獻...................................................39

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