It was noted that the formation of extended defects in graphene via the coalescence of individual mobile vacancies could significantly alter its properties. The results of ab initio simulations demonstrated that the strain created by multi-vacancy complexes in graphene determined their overall growth morphology when formed from the coalescence of individual mobile lattice vacancies. Using density functional theory, the potential energy surface for the motion of monovacancies in the vicinity of multi-vacancy defects was mapped. The inhomogeneous bond strain created by the multi-vacancy complexes strongly biased the activation energy barriers for single vacancy motion over a wide area. Kinetic Monte Carlo simulations based upon rates from ab initio derived activation energies were used to investigate the dynamic evolution of single vacancies in these strain fields. The resultant coalescence processes revealed that the dominant morphology of multi-vacancy complexes would consist of vacancy lines running in the two primary crystallographic directions, and that more thermodynamically stable structures, such as holes, were kinetically inaccessible from monovacancy aggregation alone.

Vacancy Diffusion and Coalescence in Graphene Directed by Defect Strain Fields. T.Trevethan, C.D.Latham, M.I.Heggie, P.R.Briddon, M.J.Rayson: Nanoscale, 2014, 6[5], 2978-86