A top-down approach to prepare bismuth bi-layer terminated Bi$_2$Se$_3$(0001)

A bi-layer of bismuth (Bi) in the (111) plane possesses strong spin-orbit coupling and represents a prototype 2D topological insulator (TI). In this study, we propose a novel top-down approach to prepare Bi bi-layer on 3D TI Bi$_2$Se$_3$(0001). Combining scanning tunneling microscopy, X-ray crystal truncation rod analysis and Auger electron spectroscopy we demonstrate that under controlled exposure of Bi$_2$Se$_3$ to atomic hydrogen flux the selenium is removed from the topmost quintuple layer and a flat Bi bi-layer terminated Bi$_2$Se$_3$, with Bi$_2$Se$_3$-terrace-size lateral extension is achieved. Our results suggest new prospectives to manipulate the electronic properties of both Bi and Bi$_2$Se$_3$ TIs.