Mapping the local work function and competing electronic states of two-dimensional boron/Cu(111)

Two-dimensional (2D) boron sheets have been successfully grown on a variety of metallic substrates. Among these reports, a discrepancy exists in interpreting the product of boron deposition on the Cu(111) surface, for which both borophene and 2D copper boride have been proposed. Therefore, more evidence is needed to identify the intrinsic atomic structure and electronic properties of this material system. Towards this end, we have used scanning tunneling microscopy and field emission resonance (FER) spectroscopy to systematically study the charge redistribution and potential energy of boron on Cu(111), ultimately revealing the local work function and competing electronic states with lattice resolution. The line defects of this material have also been probed and compared with density functional theory calculations. In addition to providing evidence to help resolve the debate surrounding two-dimensional boron on Cu(111), this work establishes FER spectroscopic mapping as a powerful tool that can be generalized to other 2D materials and surface science studies.