Formation of Bi x Se y Phases Upon Annealing of the Topological Insulator Bi 2 Se 3 : Stabilization of In-Depth Bismuth Bilayers.

The goal of this work is to study transformations that occur upon heating Bi ₂ Se ₃ to temperatures up to 623 K. X-ray diffraction (XRD) and scanning tunneling microscopy (STM) and spectroscopy (STS) techniques were used in our investigation. XRD was measured following the 00L and 01L truncation rods. These measurements revealed that upon heating there is a coexistence of a major Bi ₂ Se ₃ phase and other ones that present structures of quintuple-layers intercalated with Bismuth bilayers. STM measurements of the surface of this material showed the presence of large hexagonal Bi _x Se _y domains embedded in a Bi ₂ Se ₃ matrix. STS experiments were employed to map the local electronic density of states and characterize the modifications imposed by the presence of the additional phases. Finally, density functional theory (DFT) calculations were performed to support these findings.