鉍雙層在拓樸絕緣體Bi2Se3上的組成過程

Formation of a Bi bilayer on the Bi2Se3 topological insulator surface by atomic deuterium

王乃玉(Nai-Yu Wang)

指導教授 ： 林登松

國立清華大學/理學院/物理學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00239

摘要

單一鉍雙層(111)面已在理論上預測為二維拓樸絕緣體1，然而，此單一雙層鉍薄膜難以生長，因其在薄膜厚度少於四個原子層時，鉍薄膜在能量上傾向於形成黑磷結構而不是(111)面的菱形結構2-4，導致相關研究不多，因此，為了解二維拓樸絕緣體物理性質，製備單一鉍雙層(111)面是目前重點研究之一。
在此研究中，我們選擇利用將氘原子(D)曝於乾淨的Bi2Se3上，我們利用電子穿隧顯微鏡(STM)、同步輻射X射線光電子能譜(XPS) 研究表面的化學組成、表面形貌以及原子表面結構。XPS的核心能譜提供表面的化學鍵結，而STM影像提供原子尺度的表面形貌。
在曝氘原子時，XPS顯示Se 3d特徵峰強度快速減少，此極有可能為化學反應: 2D+Se→D2Se(g) 的發生造成Se原子由表面脫附，同時，在原始Bi 5d 較低鍵結能處出現一個新的特徵峰，從束縛能上之相對位置可判斷此峰應為鉍雙層，隨著D曝量的增加，新峰強度逐漸大於原本的Bi 5d 特徵鋒，最後原始的Bi 5d峰幾乎消失。而STM影像顯示，低D曝量時出現被侵蝕的三角島，最後在高曝量下，表面形成六角超結構，其中，表面下三角島的形成歸因為Se原子離開表面，而六角超結構為Bi2Se3與鉍雙層晶格差異所造成。
總結，在本研究中，我們發現了一個新的簡單方法來製備鉍雙層，且此鉍雙層為相對平整有序的結構，由此方法做出之鉍雙層可提供日後學者研究二維拓樸絕緣體的基本特性。

關鍵字

拓樸絕緣體 ； 鉍雙層 ； 氘原子

並列摘要

The single bilayer of Bi (111) has been theoretically predicted as a prototype 2D topological insulator.1 However, a bilayer film of good quality is difficult to be grown because Bi films less than 4 atomic layers in thickness prefer energetically the black-phosphorous structure instead of rhombohedral structure on substrates such as Si (001),3 Si (111),2 and HOPG.4 Therefore, it is essential to find a new method to fabricate a Bi bilayer.
In this research, we expose atomic deuterium (D) on newly cleaved Bi2Se3 surfaces. Scanning tunneling microscopy (STM) and synchrotron-radiation X-ray photoelectron spectroscopy (XPS) are employed to study the resulting surface chemical compositions, morphology, and atomic structures. Core-level spectra from XPS measurement can reveal the surface chemistry and STM can image the surfaces in real space and with atomic resolution.
After atomic D exposures, XPS shows a rapid reduction of the selenium 3d core-level intensities, suggesting strongly that Se atoms are removed via the reaction of 2D+Se→D2Se(g). In the meantime, a new component arises on the lower binding energy side of the original Bi 5d component. The binding energy shift of the two components suggests that the new component is originated from a Bi bilayer. With increasing D exposures, the new component gradually gets more intensity than the original Bi 5d component. The original one almost vanishes at large exposure. Corresponding STM images show the areas of negative islands with three-fold symmetry increases with D exposure. The final surface exhibits a hexagonal superstructure. The negative islands are attributed to the Se atoms removed from the surface while the hexagonal superstructure results from the lattice mismatch between Bi2Se3 and the topmost Bi bilayer.
In conclusion, we provide a simple new way to form a Bi bilayer. The bilayer film is reasonably smooth and ordered and can be utilized for further investigation of its electronic properties.

並列關鍵字

topological insulator ； Bi2Se3 ； Bi bilayer ； atomic deuterium

參考文獻

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