三維拓樸絕緣體是一種內部為絕緣體態、表面為導體態的新穎材料，其表面賦有如自旋－動量鎖定等等獨特的電性傳輸性質。在三維拓樸絕緣體的薄片上，藉由製做在其頂部表面的金屬接觸，這些眾多的性質已經被展示了出來，然而它們尚未藉由製做在其底部表面的金屬接觸所展示，這是因為傳統的技術無法直接地製做出這種底部的金屬接觸，而這同時也限制了垂直地研究這些性質的可能。

在此論文中，利用能將薄片移動至想要的地方的熱拾起技術，我將示範如何在從一塊碲硒化鉍銻單晶上剝離下來的三維拓樸絕緣體薄片上製做出這種底部的金屬接觸，上述的性質對於溫度、閘極電壓、垂直磁場的關係也藉由該金屬接觸得到了研究，其結果顯示底部與頂部的金屬接觸並無異處。利用絕緣且可被剝離成薄片的六方氮化硼，雙重（底部與頂部）的金屬接觸也進一步地被實做了出來，上述的性質藉由該金屬接觸得到了一部分的研究，而其結果對於如何垂直地研究這些性質有著莫大的幫助。

Three-dimensional topological insulators are novel materials with an insulating bulk state enclosed by a conducting topological surface state, endowing their surfaces with unique electrical transport properties such as spin-momentum locking. Many of the properties in ultrathin three-dimensional topological insulator flakes have been presented with the contacts fabricated on their top surfaces and edges. However, they have not been presented with the contacts fabricated on their bottom surfaces. The reason is that conventional techniques cannot be directly utilized to fabricate the bottom contacts, which also obstructs the vertical investigations of the properties.

Here I demonstrate a feasible method of fabricating bottom contacts on an ultrathin three-dimensional topological insulator flake exfoliated from a BiSbTeSe2 single crystal. It can be realized by utilizing hot pick-up technique, which can transfer ultrathin flakes onto an expected position. The temperature, gate voltage, and perpendicular magnetic field dependences of the properties are investigated with the　contacts, and the results show that there is no difference between the bottom and top contacts. The dual (bottom and top) contacts are further realized by utilizing hexagonal boron nitride, which is insulating and can be exfoliated into ultrathin flakes. Some of the properties are investigated with the contacts, and the results build a good foundation of the vertical investigations.

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