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http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17614
標題: | 奈米石墨帶的電子狀態密度與電導 Density of States and Conductances in Graphene Nanoribbons |
作者: | Yi-Cheng Lin 林奕呈 |
指導教授: | 薛文証 |
關鍵字: | 石墨烯,奈米石墨帶,鋸齒狀,手椅狀,緊束縛法,手性狀,大鋸齒狀,能帶結構,電子狀態密度,電導, graphene,graphene nanoribbons,zigzag,armchair,tight-binding method,chiral,sawtooth-like,band structure,density of states,conductance, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | 本論文的主要目的是在探討準一維無缺陷奈米石墨帶的電子狀態密度和電導。本論文之理論研究是運用緊束縛法來求得各種奈米石墨帶的能帶結構,進而得知該結構下是否具有半導體性質,例如所有的鋸齒狀奈米石墨帶皆是金屬性質,而手椅狀奈米石墨帶則只有在寬度Narm=3p+2為金屬性質,其餘寬度結構皆是具有能隙的半導體,且此能隙會隨著寬度的增加而呈現震盪性減少。此外,特別討論手椅狀奈米石墨帶邊緣鍵結氫及氫氧根之情況,發現邊緣原子的鍵結會使手椅狀奈米石墨帶之能帶結構改變,甚至會觀察到金屬性轉半導體性的現象。然而,為了進一步了解奈米石墨帶的電子特性,我們可運用所得到的能帶結構來求得各能量下的電子狀態密度及其電導。根據分析結果顯示,越平坦的能帶則會貢獻越大的電子狀態密度,而且在絕對零度下所求得的電導會具有量子化的現象,隨著溫度的增加會使量子化電導逐漸消失。然而,目前實驗上對於製造高對稱奈米石墨帶仍是粗糙,因此考慮到鋸齒狀及手椅狀混合的手性狀奈米石墨帶來貼近真實情況的奈米石墨帶。此外,我們特別考慮一大鋸齒狀奈米石墨帶的結構,在此結構下會具有更豐富的能隙結構,因而具有相對多樣的電子狀態密度及其電導特性。 The main purpose of this thesis is to investigate density of states and conductance of quasi-one-dimensional graphene nanoribbon without defects. By using the tight-binding method, one can obtain the band structure of graphene nanoribbons to know whether it exhibits a semiconducting behavior. For instance, all of the zigzag graphene nanoribbons are metallic. In contrast, armchair graphene nanoribbons are metallic only for Narm=3p+2, and other case are semiconducting. With increasing the widths of semiconducting armchair graphene nanoribbons, the size of the band gaps decreases. Moreover, one considers the case of armchair graphene nanoribbons with –H and –OH terminations. It is finded that addends can change the band structure of armchair graphene nanoribbons and even result in observable metal-to-semiconductor transition. However, in order to understand more electronic properties of graphene nanoribbon, one can use the band structures to obtain density of states and conductance spectrum. The numerical analysis shows that the flat dispersion gives rise to a sharp peak in the density of states. In addition, the conductance spectra of graphene nanoribbons exhibit quantized phenomenon at zero temperature and the quantized conductance disappear gradually as temperature increases. However, it is immature for fabricating high-symmetry graphene nanoribbons to date. Therefore, we consider chiral graphene nanoribbons which can be represented as a mixture of zigzag and armchair sites. In addition, sawtooth-like graphene nanoribbons, which are consisted of a bent angle of 120 degrees between the two zigzag edge segments, provide rich band gap structure. Thus, it can exhibit prolific density of states and transport properties. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17614 |
全文授權: | 未授權 |
顯示於系所單位: | 工程科學及海洋工程學系 |
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