The dynamics of multivacancy defects in a graphene layer were investigated by tight-binding molecular dynamics simulations and by first-principles calculation. The simulations showed that four single vacancies in the graphene layer first coalesced 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., so-called dimer diffusion, chain diffusion and single atom diffusion, were observed. Finally, the four single vacancies reconstruct into two 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. Lee, G.D., Wang, C.Z., Yoon, E., Hwang, N.M., Ho, K.M.: Physical Review B, 2006, 74[24], 245411