Binding mechanisms of molecular oxygen and moisture to graphene

We report on the binding mechanisms of oxygen and water to graphene by comparing the doping of graphene in a dry O2 environment versus in ambient. It is seen that dry oxygen dopes graphene from the basal plane while the ambient dopes graphene from the edges or from the substrate in the vicinity of the edge. Upon vacuum annealing, doping is fully reversible in the former case and only partially reversible in the latter case. We observe a thickness-dependent doping as a result of the difference in host sites for doping (basal plane versus edge). Finally, hysteresis is shown to be triggered even in dry oxygen.