Low-Temperature Growth of Bismuth Thin Films with (111) Facet on Highly Oriented Pyrolytic Graphite

The epitaxial growth of artificial two-dimensional metals at interfaces plays a key role in fabricating heterostructures for nanoelectronics. Here, we present the growth of bismuth nanostructures on highly oriented pyrolytic graphite (HOPG) under ultrahigh vacuum (UHV) conditions, which was investigated thoroughly by a combination of scanning tunneling microscopy (STM), ultraviolet photoemission spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). It was found that (111)-oriented bilayers are formed on as-cleaved high-quality HOPG at 140 K, which opens the possibility of making Bi(111) thin films on a semimetal, and this is a notable step forward from the earlier studies, which show that only Bi(110) facets could be formed at ultrathin thickness at room temperature. XPS investigation of both C 1s and Bi 4f reflects the rather weak bonding between the Bi film and the HOPG substrate and suggests a quasi layer-by-layer growth mode of Bi nanostructures on HOPG at low temperature. Moreover, the evolution of the valence band of the interface is recorded by UPS, and a transition from quantum well states to bulk-like features is observed at varying film thickness. Unlike semimetallic bulk bismuth, ultrathin Bi(111) films are expected to be topological insulators. Our study may therefore pave the way for the generation of high quality Bi nanostructures to be used in spin electronics.