Exploration of defect structures on graphene.

For graphene obtained by chemical vapor deposition, there are large amount of defects in the crystalline structures. The carbon atoms from the feedstock can attack the graphene surface in annealing process, which may be one of the reasons affecting the structure of graphene. In order to explore some defect structures on graphene, we investigate the adsorption of carbon adatoms and vacancies on graphene using first-principles calculations. It is demonstrated that the adatoms can form strong covalent bonds with the graphene and the C-C dimmer adsorption may be the most prolific defect model. The C adatom can even fill simple vacancy of graphene. Our numerical simulations also show that the defect structures can lead to the splitting of the mid-gap peak of perfect graphene in the electronic structures. It is suggested that its conductivity would be lower than that of the perfect graphene, which can explain the low mobility of the charge carriers in some experiments.