Selective Fabrication of Bismuthene and ?-Bi on Hydrogen-Terminated SiC(0001)

Nanomaterials based on monoatomic bismuth (Bi) are attracting particular attention because they are candidates of two-dimensional (2D) topological insulators and Rashba metals useful for spintronic applications. We report convenient selective fabrication of two different types of ultrathin Bi films, bismuthene and alpha-Bi on hydrogen-terminated SiC(0001), by combining the molecular-beam-epitaxy (MBE) method and the low-temperature and low-pressure hydrogen chemical etching of SiC. We have succeeded in selectively fabricating these two different Bi phases by simply tuning the substrate temperature during the MBE process. We observed that while bismuthene and alpha-Bi showed a similar low-energy electron diffraction pattern of the (root 3 x root 3)R30 degrees periodicity, angle-resolved photoemission spectroscopy revealed a sizable difference in the band structure; bismuthene shows a massive Dirac cone, a signature of 2D topological insulators, whereas alpha-Bi exhibits an insulating behavior with a large band gap of more than 1.8 eV. We discuss the underlying mechanism of selective fabrication in terms of hydrogen desorption from the hydrogen-terminated SiC substrate.