Modification of Defect Structures in Graphene by Electron Irradiation: Ab Initio Molecular Dynamics Simulations

Defects play an important role on the unique properties of the sp(2)-bonded materials, such as graphene. The creation and evolution of monovacancy, divacancy, Stone-Wales (SW), and grain boundaries (GBs) under irradiation in graphene are investigated using density functional theory and time-dependent density functional theory molecular dynamics simulations. It is of great interest that the patterns of these defects can be controlled through electron irradiation. The SW defects can be created by electron irradiation with energy above the displacement threshold energy (T-d, similar to 19 eV) and can be healed with an energy (14-18 eV) lower than Td. The transformation between four types of divacancies-V-2(5-8-5), V-2(555-777), V-2(5555-6-7777), and V-2(55-77)-can be realized through bond rotation induced by electron irradiation. The migrations of divancancies, SW defects, and GBs can also be controlled by electron irradiation. Thus, electron irradiation can serve as an important tool to modify morphology in a controllable manner and to tailor the physical properties of graphene.