Coexisting Bi and Se surface terminations of cleaved Bi2Se3 single crystals

Evidence for the coexistence of both Bi and Se terminations of the topological insulator Bi2Se3 is presented that is connected with details of sample storage and cleaving procedures. X-ray photoelectron spectroscopy of the Bi 4f core levels show a lower binding energy component indicative of metallic Bi near the sample surface. Single crystals stored and cleaved in high vacuum predominantly show the usual Se surface termination while those stored in air for long periods of time have a high probability for Bi termination. The different terminations have very different electronic structures as measured by angle resolved photoelectron spectroscopy. Our photoemission studies show the Se-terminated electronic structure can be recovered after annealing at 400 °C.