Vacancy inter-layer migration in multi-layered graphene

The migration of vacancies between graphene layers and carbon nanotube walls has been observed in experiments, in which it is well known that the migration of vacancies between adjacent layers is prohibited by a very large energy barrier (similar to 7.0 eV). This contradiction has been a major puzzle for a number of years. In the present study, by using density functional tight-binding molecular dynamic simulations and first principle calculations, we have found that interaction between vacancies or vacancy holes in neighbouring graphene layers can greatly reduce the barrier, to 3 eV or less, and this expedites the migration process. In addition, all the vacancies in a multi-layered graphene gather to form a single hole in one layer. Our study has revealed a new mechanism for healing the defect in graphene materials and successfully explains the experimental puzzle. Our results have important applications in the engineering of graphene materials.