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 ultrahigh 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 nonreproducibility of the termination.

Bismuth selenide is a two-dimensional topological insulator material composed of stacked quintuple layers (QL). The layers are held together by a weak van der Waals force that enables surface preparation by cleaving. Low energy ion scattering experiments show that Bi2Se3 cleaved under ultrahigh vacuum has a Se-terminated structure that is consistent with cleaving between QLs. Comparison of experimental data to molecular dynamics simulations confirms the Se-termination and provides an estimate of the surface relaxation.

Bi2Te3 is a topological insulator whose unique properties result from topological surface states in the band gap. The neutralization of scattered low-energy Na+, which is sensitive to dipoles that induce inhomogeneities in the local surface potential, is larger when scattered from Te than from Bi, indicating an upwards dipole at the Te sites and a downwards dipole above Bi. These dipoles are caused by the spatial distribution of the conductive electrons in the topological surface states. This result demonstrates how this alkali ion scattering method can be applied to provide direct experimental evidence of the spatial distribution of electrons in filled surface states.

Bismuth Selenide (Bi2Se3) is a topological insulator (TI) with a structure consisting of stacked quintuple layers. Single crystal surfaces are commonly prepared by mechanical cleaving. This work explores the use of low energy Ar+ ion bombardment and annealing (IBA) as an alternative method to produce reproducible and stable Bi2Se3 surfaces under ultra-high vacuum (UHV). It is found that a clean and well-ordered surface can be prepared by a single cycle of 1 keV Ar+ ion bombardment and 30 min of annealing. Low energy electron diffraction (LEED) and detailed low energy ion scattering (LEIS) measurements show no differences between IBA-prepared surfaces and those prepared by in situ cleaving in UHV. Analysis of the LEED patterns shows that the optimal annealing temperature is ~450 °C. Angular LEIS scans reveal the formation of surface Se vacancies when the annealing temperature exceeds 520 °C.