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.Comment: 31 pages, 10 figures, 1 tabl

Surface Structure of In Situ Cleaved Single Crystal Bi2Se3 Measured by Low Energy Ion Scattering

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 (LEIS) show that Bi2Se3 cleaved under ultra-high vacuum (UHV) 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.Comment: 23 pages, 6 figures, 1 tabl

Adsorptions and Reactions on Topological Insulator Surfaces Investigated by Low Energy Ion Scattering

Topological insulator (TI) materials insulate in the bulk while conduct on the surface, which makes them promising for future quantum computing and spintronics. The momentum-spin locked electron states are concentrated in the first few atomic layers, which demands a surface sensitive technique to probe. Meanwhile, the stability of the surfaces under various conditions still needs more study before TIs can be further utilized. Low energy Ion scattering (LEIS) is an extremely surface sensitive tool for investigating both surface structure and electronic properties. In this thesis, the spatial distribution of the filled topological surface states (TSS), halogen and Cs adsorption and reaction on Bi2Se3 and Bi2Te3 TI surfaces and heterostructures of bismuth bilayers on TIs are studied using LEIS and other surface analysis techniques