The dynamics of multivacancy defects in a graphene layer was investigated by tight-binding molecular dynamics simulations and by first principles calculation. The simulations showed that four single vacancies in the graphene layer first coalesce into two double vacancies, each consisting of a pentagon-heptagon-pentagon (5-8-5) defective structure. While one of the 5-8-5 defects further reconstructs into a 555-777 defect, which was composed of three pentagonal rings and three heptagonal rings, another 5-8-5 defect diffuses toward the reconstructed 555-777 defect. During the 5-8-5 defect diffusion process, three interesting mechanisms, i.e., dimer diffusion, chain diffusion and single-atom diffusion, were observed. Finally, the 4 single vacancies reconstructed into 2 adjacent 555-777 defects, which was a local haeckelite structure.

Vacancy Defects and the Formation of Local Haeckelite Structures in Graphene from Tight-Binding Molecular Dynamics. G.D.Lee, C.Z.Wang, E.Yoon, N.M.Hwang, K.M.Ho: Physical Review B, 2006, 74[24], 245411 (5pp)