Formation, structure, and bonding of boron-vacancy pairs in graphene: A first-principles study

Using density-functional theory calculations, we examine how a mobile single vacancy (V) interacts with substitutional boron (B) in graphene and the effect of boron-vacancy (BV) pairing on the electronic structure of graphene. We find that B in a BV pair energetically favors fourfold coordination, rather than remaining twofold coordinated, by forming a distorted tetrahedral structure with neighboring C lattice atoms. In the fourfold state, the binding energy of a BV pair is predicted to be 2.54 eV with respect to B and V. Our calculations also suggest magnetic-moment oscillations by interconversion between the twofold (1 μ_B) and fourfold (0 μ_B) states, as their energy difference is rather moderate (0.3eV). We also discuss the bonding mechanisms of a BV pair in the twofold and fourfold states and modifications in the electronic structure of graphene by BV pairing as compared to isolated B and V cases. Finally, the pathways and energetics of V migration in the vicinity of B are calculated; the results suggest that B is likely to trap mobile single vacancies within a certain radius and can possibly serve as an anchor for vacancy clusters.