利用傅立葉轉換掃描式穿隧電子顯微鏡研究Rashba半導體溴碲化鉍的表面電子結構

Abstract

在本篇論文中，我們探索Rashba半導體－溴碲化鉍(BiTeBr)的掃描式穿隧電子顯微鏡(Scanning Tunneling Microscopy, STM)、掃描式穿隧電子光譜(Scanning Tunneling Spectroscopy, STS)、和傅立葉掃描式穿隧電子顯微鏡(Fourier-Transform Scanning Tunneling Microscopy, FT-STM)（或稱準粒子干涉分析）的結果，並與文獻中關於此材料的化學和電子特性比較。確定本溴碲化鉍樣品為文獻中引發電子能帶產生Rashba自旋分裂的順序式結構，並發現帶有兩種不同表面缺陷的兩種極化表面，分別為正電極性的溴表面，以及負電極性的碲表面。藉由掃描式穿隧電子光譜的結果，發現在負電極性的碲表面也發現表面電子的能帶彎曲效應，使導電帶的電子能帶偏移至費米能階附近，因而產生電子的累積層。我們再以立葉掃描式穿隧電子顯微鏡作準粒子干涉分析，做出能量與表面電子布洛赫波的q值對應圖，此圖符合溴碲化鉍在文獻中角分辨光電子能譜的結果，更強而有力的給出在費米能階以上的資訊，是角分辨光電子能譜所無法測得的。然而，需要更多的計算結果來比較說明。

In this work, we combined the results of scanning tunneling microscopic, spectroscopic and the Fourier-transform scanning tunneling microscopic (also called ’quasi- particle analysis’), and the chemistry and electronic structure known from the published literatures to investigate the Rashba semiconductor BiTeBr. In the literatures, there are two kinds of crystal structure of BiTeBr, and only one of them, the ordered one has the Rashba type spin-splitting. According to our scanning tunneling microscopy topography images and comparing with the scanning tunneling spectroscopy result, two uniform polar terminations on scales exceeding 1 mm with an unit cell height difference. If the surface is positively polarized, it is the Te termination, which accompanies with the induced band bending forms an accumulation layer confining Rashba spin-splitting electrons on it. In this accumulation layer of Te-terminated surface, we observed the standing wave of the Bloch wavefunctions forms quasiparticle interference patterns, which is scattered around the surface defects. Energy and q-value dispersion relation observation shows a linear electron-like dispersion which indicates the band electrons dispersion relation of energy and wavevector. This investigation provide us more understanding of semiconductor with relativistic and strongly spin-orbit of a Rashba type spin-splitting material by the STM. But calculation results are still needed to compare with.