2010-12-012024-05-17https://scholars.lib.ntu.edu.tw/handle/123456789/682767摘要：本計畫擬利用掃描閘極顯微技術來量測石墨烯的局部電導。利用量測石墨烯的局部電導，我們可以瞭解其侷限的效應。初期的研究顯示在石墨烯的系統中，是沒有弱侷限效應的，理由是chirality會破壞時間的反轉對稱性。但是近來研究顯示在石墨烯中，不僅可能有弱侷限效應，也可能有反弱侷限效應。這可能對整個二維電子系統的研究，有重大革命性的發展。另外從Shubnikov de Haas (SdH)區域至整數量子霍爾效應的過渡過程以及絕緣態至量子霍爾態的相變，亦是整個二維電子系統的研究中懸而未決的重要議題，在石墨烯中也鮮少有關於上述研究的工作。 本計畫結合了英國劍橋大學卡文狄西實驗室史密斯教授在低溫掃描閘極顯微技術及專長與國立臺灣大學物理系梁啟德教授在侷限效應及量子相變的豐富經驗，我們是世界上最適合利用掃描閘極顯微技術來量測石墨烯的局部電導，進而研究弱侷限效應、反弱侷限效應、(SdH)區域至整數量子霍爾效應的過渡過程以及量子相變的研究團隊之一。我們相信能夠藉由執行本計畫加強台灣與英國頂尖大學的合作，也希望藉由博士生赴國外合作機構研習，培養台灣的一流研究人才，提升台灣的研究能見度與國家的在科技上的競爭力。 <br> Abstract: In this project, we plan to measure the local conductivity of a graphene flake using scanning gate microscopy. By measuring the local conductivity of a graphene, we are able to obtain useful information regarding the strength of localization and amount of disorder within the graphene system. In the pioneering work of Geim’s group, absence of weak localization in graphene has been shown. However, very recently work suggests that not only weak localization but also anitilocalization can be present in graphene. Such interesting results have been attracting worldwide interest since spin-orbit (SO) interactions, which normally give rise to antilocalization, are predicted to be very week in graphene. By using low-temperature scanning gate microscopy, we will be able shed light on both localization and antiolocalization in graphene. The crossover from the Shubnikov-de Haas (SdH) region to the integer quantum Hall regime continues to attract much interest. In the SdH regime, strong localization, which results in the integer quantum Hall effect, are expected to be unimportant. However, it has been shown that even when the magneto-resistiviy minimum approaches zero in which strong localization should be important, conventional SdH theory is still applicable, despite the fact that strong localization effects are ignored in the original theory. We plan to extend this work to graphene using scanning gate microscopy. By measuring the local conductivity of graphene, we are able to directly probe the strength of localization and hence obtain important information regarding localization and interactions in graphene. It has been suggested that the Ohmic contacts can play an important role in transport in graphene. To this end, we plan to fabricate graphene flakes on top of electrodes. In this case, even in the electrical contact regions, we are still able to measure the local conductivity of graphene using scanning gate microscopy. This important experiment should be able to able to provide crucial information regarding the role of contacts in graphene and the physics near the contact regions. This is a new area and should be rewarding in terms of research impact and research visibility.石墨烯掃描閘極顯微技術侷限效應絕緣態至量子霍爾態相變graphenenscanning gate microscopylocalization effectsinsulator-quantum Hall transition