Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers were investigated by tight-binding molecular dynamics simulations and by first principles total energy calculations. It was observed in the tight-binding molecular dynamics simulations that 2 single vacancies coalesced into a 5-8-5 double vacancy at 3000K, and it was further reconstructed into a new defect structure, the 555-777 defect, by a Stone-Wales type transformation at higher temperatures. First principles calculations confirmed that the 555-777 defect was energetically much more stable than 2 separate single vacancies, and the energy of the 555-777 defect was also slightly lower than that of the 5-8-5 double vacancy. In tight-binding molecular dynamics simulations, it was also found that the 4 single vacancies reconstructed into 2 collective 555-777 defects which was the unit for the proposed hexagonal haeckelite structure proposed.

Diffusion, Coalescence, and Reconstruction of Vacancy Defects in Graphene Layers. G.D.Lee, C.Z.Wang, E.Yoon, N.M.Hwang, D.Y.Kim, K.M.Ho: Physical Review Letters, 2005, 95[20], 205501 (3pp)