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 mu(B)) and fourfold (0 mu(B)) states, as their energy difference is rather moderate (approximate to 0.3 eV). 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.