Paper SS+AS+EM+EN-ThA7
Surface Termination of Single Crystal Bi₂Se₃ Investigated by Low Energy Ion Scattering

Thursday, October 22, 2015, 4:20 pm, Room 113

Bismuth Selenide (Bi₂Se₃) is a prototypical topological insulator (TI) with a two-dimensional layered structure that enables clean and well-ordered surfaces to be prepared by cleaving. Although some surface structure studies have concluded that the cleaved surface is terminated with Se, as is expected from the bulk crystal structure, there are other reports that show either a Bi- or mixed-termination [1]. Low Energy Ion Scattering (LEIS) and low energy electron diffraction (LEED) are used here to compare surfaces prepared by ex-situ cleaving, in-situ cleaving and Ar⁺ ion bombardment and annealing (IBA) in ultra-high vacuum. Surfaces prepared by in-situ cleaving always have a sharp 1x1 LEED patterns and are Se-terminated. Surfaces prepared by IBA show a transition from Bi- to Se-termination with increasing annealing temperature. Samples inserted into the vacuum chamber following ex-situ cleaving have much dimmer LEED patterns, show surface contamination with Auger electron spectroscopy, and could be terminated either with Se or Bi. The angular dependence of LEIS spectra, which is sensitive to the surface atomic structure, doesn’t indicate any substantial differences between surfaces prepared by IBA or in-situ cleaving. Ion scattering simulations using Kalypso are compared to experimental angular data to obtain more details about the structure. Exposure of clean surfaces to gaseous species will also be discussed in an effort to determine the surface chemical reactions responsible for the termination change.

[1] X. He, W. Zhou, Z. Y. Wang, Y.N. Zhang, J. Shi, R.Q. Wu and J.A. Yarmoff, Phys. Rev. Lett. 110, 156101 (2013).