本論文主要探討拓樸絕緣體如硒化鉍及碲化鉍於二維材料如石墨烯及單層二硫化鉬上的成長。使用二維材料做為基板的優勢是他們的表面沒有懸鍵。這對於層狀結構的材料如硒化鉍及碲化鉍成長是理想的基板。使用分子束磊晶系統，高品質薄膜可以用一個步驟在基板溫度280度及硒或碲比上鉍的比例是15到20的條件下長出來。
在硒化鉍及碲化鉍成長於石墨烯上的實驗中，清晰及非常細的反射式電子高能繞射圖案在磊晶的一開始即出現，表示我們的薄膜結晶性非常好且幾乎沒有應變。這和一般長在非凡得瓦形式的基板上的膜有很大的不同。晶體結構及品質有進一步使用反射式電子高能繞射及X光繞射確認。三角形晶域可在表面清楚的被觀察到，且硒化鉍的晶域大小約是數百奈米至一微米，而碲化鉍的晶域大小是數百奈米至二微米。清晰的拓樸絕緣體表面態也從角解析光電子能譜實驗中觀察到。
進一步拓樸絕緣體成長的研究主要是在使用單層二硫化鉬作為緩衝層於藍寶石基板上。我們將這結果與直接成長於藍寶石基板的結果做比較。二硫化鉬也是一個層狀結構的材料擁有凡得瓦形式及六重對稱的表面。大面積連續的二硫化鉬薄膜可用化學氣相沉積方法製備。和硒化鉍長在石墨烯上類似，清晰及非常細的反射式電子高能繞射圖案在磊晶的一開始即出現。而硒化鉍直接長在藍寶石基板上的前幾層就有一點模糊多晶環型的繞射出現且沒有像長在二硫化鉬上的清晰。在硒化鉍成長於二硫化鉬緩衝層的薄膜上，我們觀察到更大的三角型晶域甚至可達一點五微米、較少的螺旋狀缺線、在載子遷移率上有兩到三倍的增加、更大的SdH 震盪振幅。甚至拓樸絕緣體表面態的傳輸能從震盪中解析出來。這些證據都顯示了成長在具有凡得瓦形式基板表面的二維材料有較好的薄膜品質。

In this work, the growth of topological insulators Bi2Se3 and Bi2Te3 thin films on 2D materials of graphene/SiC, MoS2/Al2O3 was studied in details. The advantage of using 2D materials as substrates is that they do not have dangling bonds on the surface. This provides us a good template for the growth of layered materials such as Bi2Se3 and Bi2Te3. Using molecular beam epitaxy, high-quality thin films have been achieved with a single-step growth method at a substrate temperature (Ts) 280℃ with the Se (or Te) to Bi flux ratio kept at 15-20.
For Bi2Se3 and Bi2Te3 films grown on graphene/SiC, sharp and streaky RHEED patterns showed up at the first layer of growth, suggesting that the crystallinity of the films were good and they were almost strain free. This is the main difference between Bi2Se3 and Bi2Te3 on other non van der Waals type substrate surface. The crystal quality and structure were further checked by synchrotron radiation X-ray diffraction. Clear triangular domain with the size of a few hundreds nm to 1μm for Bi2Se3 and a few hundreds nm to 2μm for Bi2Te3 were observed. Sharp surface states were found in ARPES measurement.
Further study of TI growth is focused on using the MoS2 monolayer as a growth buffer on Al2O3. The result is compared to the one directly grown on Al2O3.¬ MoS2 is a layered material which has van der Waals type surface without dangling bonds, having a hexagonal symmetry surface. Large and continuous MoS2 films can be grown using CVD. At the initial growth stage of Bi2Se3 on MoS2/Al2O3, streaky diffraction rods showed up which was similar to the ones on graphene/SiC. For Bi2Se3 directly on Al2O3, it has a blur polycrystalline ring and the diffraction is not as sharp as the one on MoS2 buffer at the first few QLs. Larger triangular domain size up to 1.5μm, less spiral defects, about 2-3 time enhancement in mobility and stronger SdH oscillation amplitude were observed in films with MoS2 buffer. Moreover, topological surface state transport was found by fitting the SdH oscillation curve. These all indicate that the film quality can be improved by using 2D materials with van der Waals type substrate surface.

Abstract i
Acknowledgement v
Contents vi
List of figures viii
List of tables xi
Chapter 1 Introduction 1
1.1 Introduction of topological insulator 1
1.1.1 Two dimensional topological insulator (2D TI) 2
1.1.2 Three dimensional topological insulator (3D TI) 3
1.2 Material properties of Bi2Se3 and Bi2Te3 4
1.3 Van der Waals epitaxy 5
1.4 Motivation 7
Chapter 2 Instrumentations 8
2.1 Sample Growth 8
2.1.1 Molecular beam epitaxy (MBE) 8
2.2 Characterization 9
2.2.1 Reflection high energy electron diffraction (RHEED) 9
2.2.2 Atomic force microscopy (AFM) 10
2.2.3 X-ray diffraction (XRD) 12
2.2.4 Raman spectroscopy 12
2.2.5 Angle-resolved photoemission spectroscopy (ARPES) 14
2.2.6 Transport properties measurement 15
2.2.7 Hall measurement 16
Chapter 3 Results and discussions I: Bi2Se3 and Bi2Te3 on epitaxial graphene/SiC 19
3.1 Epitaxial graphene 19
3.1.1 Growth 19
3.1.2 Raman spectroscopy 21
3.1.3 ARPES study 23
3.1.4 Surface morphology 24
3.1.5 Structural analysis 25
3.2 Bi2Se3 and Bi2Te3 on epitaxial graphene 26
3.2.1 Growth 26
3.2.2 Structural analysis 27
3.2.3 Surface morphology 31
3.2.4 ARPES study 32
3.3 Summary 33
Chapter 4 Results and discussions II: A comparative study of Bi2Se3 on Al2O3 and MoS2/Al2O3 34
4.1 Substrate preparation and characterization 34
4.1.1 Al2O3(0001) substrate 34
4.1.2 Monolayered-MoS2 on Al2O3(0001) 34
4.2 Bi2Se3 on Al2O3 and MoS2/Al2O3 37
4.2.1 Growth 37
4.2.2 Structrual analysis 38
4.2.3 Surface morphology 41
4.2.4 Transport property study 42
4.2.5 ARPES study 48
4.3 Summary 48
Chapter 5 Conclusion 50
References 51

References
[1] C. Jozwiak, Y. L. Chen, A. V. Fedorov, J. G. Analytis, C. R. Rotundu, A. K. Schmid, J. D. Denlinger, Y.-D. Chuang, D.-H. Lee, I. R. Fisher, R. J. Birgeneau, Z.-X. Shen, Z. Hussain, and A. Lanzara, Phys. Rev. B 84, 165113 (2011)
[2] B. A. Bernevig, T. L. Hughes, and S. C. Zhang, Science 314 (5806), 1757 (2006).
[3] M. König, S. Wiedmann,C. Brüne, A. Roth, H. Buhmann, L. Molenkamp, X. L. Qi and S. C. Zhang, Science 318 (5851), 766 (2007).
[4] X. L. Qi and S. C. Zhang, Phys. Today 63 (1), 33 (2010).
[5] L. Fu, C. L. Kane, and E. J. Mele, Phys. Rev. Lett. 98 (10), 106803 (2007).
[6] F. Liang and C. L. Kane, Phy. Rev. B 76 (4), 045302 (2007).
[7] D. Hsieh, D. Qian, L. Wray, Y. Xia, Y. S. Hor, R. J. Cava, and M. Z. Hasan, Nature 452 (7190), 970 (2008).
[8] H. Zhang, C. X. Liu, X. L. Qi, X. Dai, Z. Fang, and S. C. Zhang, Nat. Phys. 5 (6), 438 (2009).
[9] Y. L. Chen, J. G. Analytis, J. H. Chu, Z. K. Liu, S. K. Mo, X. L. Qi, H. J. Zhang, D. H. Lu, X. Dai, Z. Fang, S. C. Zhang, I. R. Fisher, Z. Hussain, and Z. X. Shen, Science 325 (5937), 178 (2009).
[10] Y. Zhang, K. He, C. Z. Chang, C. L. Song, L. L. Wang, X. Chen, J. F. Jia, Z. Fang, X. Dai, W. Y. Shan, S. Q. Shen, Q. Niu, X. L. Qi, S. C. Zhang, X. C. Ma and Q. K. Xue, Nat. Phys. 6, 584 (2010).
[11] A. Koma, K. Sunouchi, and T. Miyajima, Microelectronic Enngineering 2, 129 (1984).
[12] A. Koma, Thin Solid Films 216, 72 (1992).
[13] A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).
[14] M.-H. Xie, X. Guo, Z.-J, Xu and W.-K Ho, Chin. Phys. B 22(6), 068101 (2013).
[15] N. Bansal, Y. S. Kim, M. Brahlek, E. Edrey and S. Oh, Phys. Rev. Lett., 109, 116804 (2012).
[16] N. Bansal, Y. S. Kim, E. Edrey, M. Brahlke, Y. Horibe, K. Lida, M. Tanimura, G. H. Li, T. Feng, H. D. Lee, T. Gustafsson, E. Andrei, and S. Oh, Thin Solid Films 520, 224 (2011).
[17] N. Koirala, M. Brahlek, M. Salehi, L. Wu, J. Dai, J. Waugh, T. Nummy, M.-G. Han, J. Moon, Y. Zhu, D. Dessau, W. Wu, N. P. Armitage and S. Oh, Nano Lett. 15(12), 8245–8249(2015).
[18] P. Frigeri, L. Seravalli, G. Trevisi, S. Franchi, Comprehensive Semiconductor Science and Technology, 480-522, Molecular Beam Epitaxy: An Overview (2011).
[19] http://www.parkafm.com/index.php/park-spm-modes/standard-imaging-mode/217-true-non-contact-mode
[20] https://www3.nd.edu/~kamatlab/facilities_spectroscopy.html
[21] A. Damascelli, Physica Scripta. T109, 61 (2004).
[22] K. V. Emtsev, A. Bostwick, K. Horn, J. Jobst, G. L. Kellogg, L. Ley, J. L. McChesney, T. Ohta, S. A. Reshanov, J. Röhrl, E. Rotenberg, A. K. Schmid, D. Waldmann, H. B. Weber and T. Seylle, Nature Materials 8, 203 (2009).
[23] D. S. Lee, C. Riedl, B. Krauss, K. von Klitzing, U. Starke and J. H. Smet, Nano Lett., 8(12), 4320 (2008).
[24] Y. H. Lee, L. Yu, H. Wang, W. Fang, X. Ling, Y. Shi, C. Lin, M. Chang, C. Chang, M. Dresselhaus, T. Palacios, L. Li and Jing Kong, Nano Letters, 13(4), 1852–1857 (2013).