三維的拓樸絕緣體是一種新穎的半導體材料，它的表面可以進行電子傳輸而材料的內部相對於表面則是絕緣態，表面態的電子傳輸受到時間反轉對稱性的保護。拓樸絕緣體的表面態在近年來被廣泛的研究，但絕緣態大多都從表面態的實驗中進而用理論去推導出來。那最主要的原因就是在傳統的製程以及量測下，無法準確的區分表面態跟絕緣態的獨立性。

在這個實驗中，我們展現一種新類型的製程。我們做出了電路分別接觸上以及下的表面態而沒接觸到絕緣態的部分。一開始先利用蒸鍍的方法把下電路鍍到基板上，接下來再利用機械剝離法以及乾式轉移的技術可以準確地把樣品放在一開始鍍好的電路上。一樣用乾式轉移的技術把氮化硼轉移到樣品的邊緣，而絕緣性良好的氮化硼的功用就是避免讓上電路直接接觸到樣品的側面。最後在把上電路鍍在樣品上，而我們可以藉由這樣的電路設計，進而在低溫下獨立的量測表面態以及絕緣態的性質。

Three-dimensional topological insulator(TI) is a material with bulk insulation and surface conduction which are protected by time-reversal symmetry. Although surface state of TI has been extensively studied in ARPES, there have been not many studies in its transport properties. One of the major reasons is that it is difficult to well distinguish the surface transport from the bulk contribution in conventional electrical detection setup.

Here, we show a new type of device with contacts on both the top and bottom surfaces. Firstly, we deposited the metallic back-contact on a heavily-doped Si/SiO2 substrate, then use mechanical exfoliation to exfoliate undoped Bi2Se3 upon the back-contact and use dry transfer technique to pick up BN on the sample edge. The BN is an insulating layer which prevent the contact from touching the edge and bottom-surface state. Finally, we put the top-contact on the Bi2Se3 flake. By tuning back-gate voltage, we study the electron transport along the surface and also through the bulk at the same time with our device design.

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