Atomically Smooth Ultrathin Films of Topological Insulator Sb₂Te₃

The growth and characterization of single-crystalline thin films of topological insulators (TIs) is an important step towards their possible applications. Using in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), we show that moderately thick Sb₂Te₃ films grown layer-by-layer by molecular beam epitaxy (MBE) on Si(111) are atomically smooth, single-crystalline, and intrinsically insulating. Furthermore, these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states. Depositing Cs in situ moves the Fermi energy of the Sb₂Te₃ films without changing the electronic band structure, as predicted by theory. We found that the TI behavior is preserved in Sb₂Te₃ films down to five quintuple layers (QLs).