Hydrogen induced contrasting modes of initial nucleations of graphene on transition metal surfaces.

Our first-principles calculations reveal that there exist contrasting modes of initial nucleations of graphene on transition metal surfaces, in which hydrogen plays the role. On Cu(100) and Cu(111) surfaces, an sp(2)-type network of carbons can be automatically formed with the help of hydrogen under very low carbon coverages. Thus, by tuning the chemical potential of hydrogen, both of the nucleation process and the following growth can be finely controlled. In contrast, on the Ni(111) surface, instead of hydrogen, the carbon coverage is the critical factor for the nucleation and growth. These findings serve as new insights for further improving the poor quality of the grown graphene on transition metal substrates.