Termination of Single Crystal Bi2Se3 Surfaces Prepared by Various   Methods
  Bismuth Selenide (Bi2Se3) is a topological insulator with a two-dimensional layered structure that enables clean and well-ordered surfaces to be prepared by cleaving. Although some studies have demonstrated that the cleaved surface is terminated with Se, as expected from the bulk crystal structure, other reports have indicated either a Bi- or mixed-termination. Low energy ion scattering (LEIS), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) are used here to compare surfaces prepared by ex situ cleaving, in situ cleaving, and ion bombardment and annealing (IBA) in ultra-high vacuum (UHV). Surfaces prepared by in situ cleaving and IBA are well ordered and Se-terminated. Ex situ cleaved samples could be either Se-terminated or Bi-rich, are less well ordered and have adsorbed contaminants. This suggests that a chemical reaction involving atmospheric contaminants, which may preferentially adsorb at surface defects, could contribute to the non-reproducibility of the termination. 
Weimin Zhou, Haoshan Zhu, Jory A. Yarmoff
cond-mat.mtrl-sci