Surface potential dependence of the topological insulator Bi2Se3 studied by scanning photoemission and Kelvin probe microscopy

The atomic composition and electronic structure of topological insulators (TI) Bi2Se3 grown by the twotemperature Physical Vapor Deposition on n-type Si patterned substrates, have been followed in details during slight variations of the growth temperatures and values of thickness close to that of the topological transition (about 6 nm), by means of submicron lateral probe photoemission with enhanced surface sensitivity (less than 1 nm). Raman and atomic force microscopy together with Kelvin probe microscopy provide a coherent picture where the fine tuning of Se doping and of the growth temperatures constrain the on–set of the gapless state at the exact middle point of the gap.