建立自旋角解析光電子譜實驗站與對Au(111) 與Bi2Se3表面態能帶的量測

本論文實驗在於使用Au(111) 與Bi2Se3 表面態來檢測新建立的自旋與角解析光電子能譜(Spin- and Angle-Resolved Photoemission Spectroscopy, SARPES)系統，本實驗站系統採用新式半球分析儀搭配VLEED自旋偵測器的系統。實驗站建立完成後，第一個檢測樣品為Au(111)表面，此系統為表面科學界非常了解的系統，Au(111)表面有明顯的Rashba效應(Rashba effect)，由Rashba效應所引起的能帶分裂是很好的檢測素材，為了更了解其系統細節，將使用常見的拓樸絕緣體Bi2Se3來進行檢測，拓樸絕緣體由於其效應會造成表面態能帶反轉，而會產生線性的交叉線能帶有不同的自旋分量，亦可檢測其自旋系統，測試不同狹縫及不同光圈下分析儀的表現，最終自旋測量的結果。此次實驗三維(kx,ky,E)能帶繪圖結果發現在於偏折方向上解析度明顯不比狹縫所接受角度，由金的分析可發現kx方向上可控制在0.01 Å^(-1)，而ky選取較好的範圍也僅能控制在0.012 Å^(-1)，而判斷自旋偵測儀的效率為品質因數(figure of merit, FOM)，傳統的自旋偵測器為Mott其品質因為約為1~5×10^(-4)，而此次測量VLEED在不同的散射能量得到最高約為1.6×10^(-2)，其效率比傳統的自旋偵測器高出兩個數量級，自旋偵測器測量雖然可區分不同的自旋分量，但無法將自旋完美分隔，試算偏極化結果發現背景訊號過強，推測可能是因為光點太大以及光強度不足，導致量測的被能帶與背景訊號對比不強烈，整體強度偏低。本實驗了解自旋偵測儀系統整體使用情況，在日後使用時可以有個參考依據，本篇論文也簡易的描繪了常用的儀器之使用步驟，希望在未來使用上能夠減少花費時間去摸索，能夠在最短的時間內上手進行實際操作。

關鍵字

自旋角解析光電子能譜；拓樸絕緣體

並列摘要

The work described in this thesis is to construct a Spin- and Angle-Resolved Photoemission Spectroscopy (SARPES) Endstation in the Taiwan Photon Source and to reexamine the spin-texture and band structure of the surface state of Au(111) and Bi2Se3 surfaces as model systems. The power horse of this endstation is equipped with a 200-mm-radius three-dimensional hemispherical analyzer and an integrated Very Low-Energy Electron Diffraction (VLEED) spin detector. After the construction was finished, the first test was the surface of the Au(111) which is relatively well studied in the last decade. Its surface state band’s spin degeneracy is removed due to the Rashba effect. This is the reason of the surface of the Au(111) is a good material for test. To characterize further the SARPES system, we invested another prototypical topological insulator Bi2Se3. The characteristic of this topological insulator is the band inversion to form a linear surface state. The surface state band shows a different spin component at different E-K spaces, so it also can be used to test the spin system. The measurements of the 3D (kx, ky, E) mapping indicate the resolution of kx is better than the resolution of ky. The resolution of kx is about 0.01(Å^(-1))and the resolution of ky is about 0.012(Å^(-1)) by analyzing the data of the Au(111). The factor for judge the efficiency of the spin detector is the figure of merit (FOM). The FOM of the traditional spin detector Mott is about 1~5×10^(-4), but the FOM of the VLEED spin detector is about 1.6×10^(-2). The result indicated the VLEED increase in efficiency by two orders of magnitude. The spin detector can distinguish two different spin components, but it can’t perfectly separate two different spin components. We also tried to calculate the spin polarization. We found the background signal very strong. We speculate the intensity of light source is insufficient, leading to the contrast background signal with band signal which is not powerful as we hoped for. Through experiments we completely realize the SARPES system operational condition. It can be a reference in the future. This thesis also includes a practical instruction of the user’s operation of SARPES. We hope in the future one can able to use this system correctly in a shortest time.

並列關鍵字

SARPES ； topological

參考文獻

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建立自旋角解析光電子譜實驗站與對Au(111) 與Bi2Se3表面態能帶的量測

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