Metallicity retained by covalent functionalization of graphene with phenyl groups.

To resolve the controversy over the functionalization effect on conductivity, we systematically investigate the structural and electronic properties of graphene covalently functionalized with phenyl groups. Using first-principles calculations combined with the model Hamiltonian analysis, we find that the structural stability, electronic and transport properties of the functionalized graphene are strongly dependent on the adsorption site of the phenyl groups. In detail, double-side functionalized graphene is energetically more favorable than single-side functionalized graphene, and more importantly, they exhibit an exotic non-magnetic metallic state and a magnetic semiconducting state, respectively. For covalently double-side functionalized graphene, two bands contributed by π electrons of graphene cross at the Fermi level with the preserved electron-hole symmetry, and the Fermi velocity of carriers could be flexibly tuned by changing the coverage of the phenyl groups. These results provide an insight into the experimental observation [ACS Nano 2011, 5, 7945], interpreting the origin of the increase in the conductivity of graphene covalently functionalized with phenyl groups. Our work reveals the great potential of these materials in future nanoelectronics or sensors by controlling the attachment of phenyl groups.