Ab Initio Calculations of Bonding and Charge Transfer in Borophene Sheets on a Cu(111) Substrate

Borophene, the two-dimensional hexagonal lattice form of boron, is predicted to have technological uses in flexible electronics and as a precursor to metallic boron nanotubes. Boron’s electron deficiency leads to borophene sheets that have both hexagonal and triangular bonding, and different arrangements of these motifs lead to a wide range of nearly isoenergetic phases. Previous work has grown boron on Ag(111) substrates and reported the striped β₁₂ and χ₃ borophene phases, but more recent growth on a Cu(111) substrate by our team describes a more complex sheet structure with a much larger unit cell. We describe ab initio density functional theory simulations of borophene sheets on the Cu(111) surface to understand and explain this observed lattice structure. We discuss the bonding structure within the borophene sheet, paying special attention to electron doping via charge transfer from the Cu substrate. In addition, we compare our results to calculations of free-standing borophene sheets and discuss implications for practical growth of borophene on substrates.

R. Wu et al., “Large-area single-crystal sheets of borophene on Cu(111) surfaces”, Nature Nanotechnology 14, 44-49 (2019)