  The conversion of multilayer graphenes into sp^3-bonded carbon films on metal
surfaces (through hydrogenation or fluorination of the outer surface of the top
graphene layer) is indicated through first-principles computations. The main
driving force for this conversion is the hybridization between carbon sp^3
orbitals and metal surface dz^2 orbitals. The induced electronic gap states in
the carbon layers are confined in a region within 0.5 nm of the metal surface.
Whether the conversion occurs depend on the fraction of hydrogenated
(fluorinated) C atoms and on the number of stacked graphene layers. In the
analysis of the Eliashberg spectral functions for the sp^3 carbon films on
diamagnetic metals, the strong covalent metal-sp^3 carbon bonds induce soft
phonon modes that predominantly contribute to large electron-phonon couplings,
suggesting the possibility of phonon-mediated superconductivity. Our results
suggest a route to experimental realization of large-area ultrathin sp^3-bonded
carbon films on metal surfaces.
