Epitaxial fabrication of topological Bi-Sb alloy films by surface alloying of Sb nanofilms

Abstract

The bismuth-antimony (Bi-Sb) alloys with some specific Sb concentrations are three-dimensional topological insulators (3D TIs). For the thin Bi-Sb alloy films, the quantum confinement effect can suppress the bulk conduction channels and enhance the transport of the topological surface states. However, the fabrication of Bi-Sb films is still challenging. Here, we have successfully prepared the Bi-Sb alloy films by surface Bi-alloying of the epitaxial Sb nanofilm on highly oriented pyrolytic graphite (HOPG) substrate. The morphology, atomic structure, and electronic structure of the Bi-Sb alloy films were characterized by a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy/spectroscopy (STM/STS). The formation of hexagonal Bi-Sb surface alloy was confirmed by the atomic-resolution STM images. The quantum-well states (QWS) were directly observed in the STS spectra of Bi-Sb films due to the strong quantum confinement effect. The standing-wave patterns of QWS are further observed in the real-space spectra maps. Our work suggests a promising route to fabricate Bi-Sb alloy films and lays the foundation for further exploring their topological electronic structures.