根據理論計算，單一雙層(bilayer)或兩個雙層的鉍化鎵及鉍化銦薄膜為一種具有很大能隙的二維拓樸絕緣體[1-3]，這種大能隙的二維拓樸絕緣體有別於過去所發現的，其量子阱體系在室溫環境會受限於能隙過小而不復存，因此這樣的發現讓我們想繼續進行實驗上的研究。其中(鉍,銦)在Si(111)晶面上的成長模式已經於2016年3月，Denisov等人的實驗研究初步建立[4]，而至今尚未有關於成長鉍化鎵薄膜的研究發表，因此我們嘗試成長，考慮Ge(111)-(2×2)與計算的鉍化鎵薄膜(√3×√3)的晶格常數相當地接近，我們決定選用Ge(111)為成長的基板。
本研究使用掃描穿隧式電子顯微鏡觀察樣品表面形貌變化，並用X射線光電子能譜儀來分析樣品表面原子間鍵結的變化，兩者相輔，我們可以清楚了解樣品表面在成長過程中所發生的現象。
實驗中主要以三種成長方式來嘗試，分別是：一、在鎵/Ge(111)表面沉積鉍、二、在鉍/Ge(111)表面沉積鎵、三、在Ge(111)晶面同時沉積鉍與鎵。在第一種成長方式，於400 ℃退火時，表面出現了(√3×√3)結構，此結構區域傾向沿著臺階邊緣出現，在進一步的研究後發現，此結構並非為鉍化鎵薄膜，而是鉍原子取代鎵原子並與鍺原子鍵結所形成。我們完成三種成長方式的嘗試發現，鎵原子層在Ge(111)晶面的結構並不穩定，其鍵結會遭吸附的鉍原子破壞；鉍原子層在Ge(111)則晶面的結構則較為穩定，但其難以與鎵原子反應，造成樣品在200-250℃退火期間形成許多三維島嶼，並在樣品經更高溫退火後形成巨大的原子團。我們探討三種成長方式過程中表面的變化，最後整理成簡易的模型來清楚呈現。
總結，此三種成長方式，並沒有成功成長出鉍化鎵的二維薄膜，然而，本篇論文中探討了過程中表面發生的各種現象如：鉍取代鎵的過程、鎵的三維島嶼形成、鎵在Ge(111)的相變、鎵侵蝕Ge(111)基板的現象等等，從中更加了解鎵與鉍原子在Ge(111)表面的特性，這些成果將帶給未來繼續嘗試成長鉍化鎵薄膜研究的學者們一些依據。

Up to date, 2D topological insulators found are limited to the quantum well systems which have small band gaps and do not survive at room temperature. A recent theoretical calculation shows that GaBi and InBi films of one or two bilayer thick are 2D topological insulators with large band gaps. This finding encourages us to proceed this experimental study. Growth of (In,Bi) thin film study was initially accomplished by Denisov et al. So far, Growth of GaBi thin film has not been carried out experimentally.
Because the lattice constant of Ge(111)-(2×2) is very close to that of the calculated GaBi-(√3×√3), we chose the Ge(111) wafer as the substrate in this study. After the growth, we use scanning tunneling microscopy to observe the evolution of the surface morphology, and X-ray photoemission spectroscopy to analyze the chemical shift of various surface species. These two techniques are complementary to each other, allowing us to understand the phenomenon on the sample surface during growth.
Three growth method are employed in this experiment:1. Deposit Bi on Ga/Ge(111).”, “2. Deposit Ga on Bi/Ge(111).”, “3. Co-deposit Ga and Bi on Ge(111).” In method 1, the surface exhibits (√3×√3) structure after annealing to 400 ℃. The (√3×√3) domains prefer to grow along the steps. With further investigation, we find this structure is not the GaBi thin film. Instead, it consists Bi adatoms that replace the Ga atoms and bond with Ge substrate. In other words, the Ga-Ge bonds is replaced by Bi-Ge ones upon Bi adsorption. The structure of Bi thin film on Ge(111) is more stable, but it is difficult to for Ga adsorption. Subsequential Ga adsorption form many 3D islands upon 200-250℃ annealing and large clusters at enen higher temperature. Finally, we discuss the evolution in three growth method and organize them to simple models.
In summary, neither of these three growth methods succeeded to form GaBi films. In this thesis, we discussed some phenomenon in the process of growth, including “the Bi atom replace the Ga atom”, “the Ga 3D islands formed”, “phase transition in Ga/Ge(111)” , and “Ge(111) substrate etched by Ga”. We realized more details about properties of Bi and Ga atoms on the surface. The knowledge acquired herein could help further investigation of this new material. .

[1] C. P. Crisostomo, L. Z. Yao, Z. Q. Huang, C. H. Hsu, F. C. Chuang, H. Lin, M. A. Albao, and A. Bansil, Nano letters 15, 6568 (2015).
[2] L. Z. Yao, C. P. Crisostomo, C. C. Yeh, S. M. Lai, Z. Q. Huang, C. H. Hsu, F. C. Chuang, H. Lin, and A. Bansil, Scientific reports 5, 15463 (2015).
[3] F. C. Chuang, L. Z. Yao, Z. Q. Huang, Y. T. Liu, C. H. Hsu, T. Das, H. Lin, and A. Bansil, Nano letters 14, 2505 (2014).
[4] N. V. Denisov, A. A. Alekseev, O. A. Utas, S. G. Azatyan, A. V. Zotov, and A. A. Saranin, Surface Science 651, 105 (2016).
[5] C. L. Kane and E. J. Mele, Phys Rev Lett 95, 146802 (2005).
[6] J. E. Moore and L. Balents, Physical Review B 75 (2007).
[7] D. J. Chadi and C. Chiang, Physical Review B 23, 1843 (1981).
[8] R. S. Becker, B. S. Swartzentruber, J. S. Vickers, and T. Klitsner, Physical Review B 39, 1633 (1989).
[9] E. S. Hirschorn, D. S. Lin, F. M. Leibsle, A. Samsavar, and T. C. Chiang, Physical Review B 44, 1403 (1991).
[10] I. Razado-Colambo, J. He, H. M. Zhang, G. V. Hansson, and R. I. G. Uhrberg, Physical Review B 79 (2009).
[11] X.-L. Q. a. S.-C. Zhang, Physics Today (January,2010).
[12] M. A. D.M. Li, T. Okamoto, T. Tambo, C. Tatsuyama *, Surface Science 417, 210 (1998).
[13] D. V. G. Bommisetty V. RAO, Toyokazu TAMBO and Chiei TATSUYAMA, Jpn.J Appl. Phys. 40, 4304 (June ,2001).
[14] S. Hatta, T. Aruga, Y. Ohtsubo, and H. Okuyama, Physical Review B 80 (2009).
[15] A. Goriachko, P. V. Melnik, A. Shchyrba, S. P. Kulyk, and M. G. Nakhodkin, Surface Science 605, 1771 (2011).
[16] M. Böhringer, P. Molinàs-Mata, E. Artacho, and J. Zegenhagen, Physical Review B 51, 9965 (1995).
[17] P. Molinàs-Mata, M. Böhringer, and J. Zegenhagen, Surface Science 317, 378 (1994).