Bi2Se3 Topological Insulator 형성 및 물성 연구

Abstract

We have investigated the formation and physical properties of a Bi2Se3 topological insulator (TI). We have utilized an in-situ self-assembly method to form a Bi2Se3 film by evaporating two sources, bismuth(Bi) and selenium(Se) on the Si(111)-7x7 surface at room temperature under a UHV environment. We have used a low-energy-electron diffraction (LEED) to probe the structural changes during the formation of the TI, and angle-resolved photoemission spectroscopy (ARPES) to measure its electronic band structures. We have identified the formation of one quintuple layer (QL) when a strong 1x1 LEED pattern appears. By delicately controlling the growth condition, we observed the formation of the Bi2Se3 TI film through QL-by-QL growth. We find that upon depositing one monolayer (ML) of Bi on the Si(111) surface, the surface becomes a x phase eliminating all the dangling bonds of the Si(111) surface although not confirmed if the phase is of or . We have carefully monitored the change of intensity of the (10) LEED spot as a function of Bi coverage to confirm the coverage of 1ML, which is important to form the Bi2Se3 TI. As the number of QL increases while forming the TI, we also notice the change in the atomic spacing through the intensity profile between two normal LEED spots. Our electronic band structure measured by using ARPES reveals the single surface Dirac cone of the Bi2Se3, typical for a TI, which agrees well with those reported earlier. The band inversion during the growth of the film is found to occur between two and three QL’s caused by the change in the distance between the top and the bottom surfaces of the film. Such a feature has been supported both by the reversed band gap and also by a band fitting parameter.