Hybridization versus sublattice symmetry breaking in the band gap opening in graphene on Ni(111): A first-principles study

Abstract

Band gap opening in graphene (Gr) on metals has been ascribed to hybridization, sublattice symmetry breaking (SSB), or conbinations of both. However, how and to what extent band gap opens under the influence of these effects is not well understood and is still a question in controversy. In this paper, we use first-principle calculations to elucidate this controversy by focusing on Gr/Ni(111), which provides an ideal platform for the present study owing to a (1 × 1)-commensurate structure resulting from negligible lattice mismatch. Electronic structures of artificially expanded or compressed systems with larger and smaller Gr-Ni(111) separations (d) than the equilibrium one (deq) are interpolated to find characteristics of band gap opening in Gr/Ni(111) with d ≈ deq. Similarities and differences among the top-hcp, top-fcc and bridge-top structures are also fully utilized in the analyses based on an additive model. We find that the band gap in Gr in the brigde-top structure is rather small, which can be explained by the absence of SSB in this structure. On the other hand, band gaps in Gr are much larger in the top-hcp and top-fcc structures, in which SSB is the strongest among possible structures. We have successfully discriminated, for the first time, the effects of hybridization and SSB on the band gap opening in these structures from each other and found that both effects are comparable for d ≈ deq and together induce band gaps of ~ 400meV, which are about four times as large as that in the bridge-top structure. These results provide a clear understanding of the band gap opening in Gr/Ni(111) and, though not directly applicable, would provide a useful insight into the band gap opening in other Gr/metal superstructures resulting from lattice mismatch, intercalation, or other modifications.