How water makes graphene metallic

A simple explanation is given on the tendency of graphene to become metallic when the amount of doped water is increased, an effect which was previously obtained from ab initio band calculations. It is clarified how the effect is mainly determined by oriented water electric dipoles, which create a step like potential at the separation distance between graphene and water planes. By using perturbation theory and an effective potential coupled with a image-charge tail potential, we showed that under increasing the water doping, the lowest energy free band in graphene starts lowering their energies by approaching to the Fermi level. Moreover, we demonstrated that this crossing induces a huge increase of states at the Fermi level, an effect akin to the magic-angle flat-band appearance in bilayer graphene.