Stability of the (0001) surface of the Bi$^2$Se$^3$ topological insulator

The inertness of the cleaved (0001) surface of a Bi$_{2}$Se$_{3}$ single crystal to oxidation has been demonstrated using X-ray photoelectron spectroscopy, as well as atomic-force and scanning tunneling microscopy and spectroscopy. No intrinsic bismuth and selenium oxides are formed on the surface after a month of storage in air. Atomically flat surfaces with macroscopic sizes (${\sim}\,1\,$cm$^2$) and rms roughness less than $0.1$ nm have been prepared, and (1$\times$1)-(0001) Bi$_{2}$Se$_{3}$ atomic structure has been resolved. The tunneling conductance measurements have shown that the energy dependence of the surface density of states is quasilinear in the band gap of Bi$_{2}$Se$_{3}$.