Graphene layer formation on polycrystalline nickel grown by chemical vapor deposition

We studied the structure of graphene layers grown by chemical vapor deposition on polycrystalline nickel. The conditions of the polycrystalline nickel catalyst (size of fine crystals and surface roughness) were controlled by cyclic heating and cooling, and its effect on the graphene layer formation was evaluated. By increasing the average size of the nickel fine crystals and thereby increasing of the surface roughness, nonuniformity of the graphene sheet numbers tends to increase. A marked change in graphene sheet number tends to occur at discontinuities in the polycrystalline nickel surfaces. From the structural analysis, the graphene layer is found to be made up of single or multiple crystal graphene thin films with different crystallographic directions. The size of each thin film is independent of and not restricted by the size of the nickel fine crystals, and a certain thin film passes over the discontinuities.