Electrical control of the chemical bonding of fluorine on graphene

We study the electronic structure of diluted F atoms chemisorbed on graphene using density functional theory calculations. We show that the nature of the chemical bonding of a F atom adsorbed on top of a C atom in graphene strongly depends on carrier doping. In neutral samples the F impurities induce a sp3-like bonding of the C atom below, generating a local distortion of the hexagonal lattice. As the graphene is electron-doped, the C atom retracts back to the graphene plane and for high doping (1014 cm^-2) its electronic structure corresponds to a nearly pure sp2 configuration. We interpret this sp3-sp2 doping-induced crossover in terms of a simple tight-binding model and discuss the physical consequences of this change.