Using angle resolved photoemission spectroscopy we studied the evolution of the surface electronic structure of the topological insulator Bi2Se3 as a function of water vapor exposure. We find that a surface reaction with water induces a band bending shifting the Dirac point deep into the occupied states and creating quantum well states with a strong Rashba-type splitting. The surface is thus not chemically inert, but the topological state remains protected. The band bending is traced back to Se-abstraction leaving positively charged vacancies at the surface. Due to the presence of water vapor, a similar effect takes place when Bi2Se3 crystals are left in vacuum or cleaved in air, which likely explains the aging effect observed in the Bi2Se3 band structure.
@article{arxiv.1105.2664,
title = {Reactive chemical doping of the $Bi_2 Se_3$ topological insulator},
author = {Hadj M. Benia and Chengtian Lin and Klaus Kern and Christian R. Ast},
journal= {arXiv preprint arXiv:1105.2664},
year = {2011}
}