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Graphene synthesis from graphite/Ni composite films grown by sputtering

Graphite/Ni composite films have been deposited on SiO2/Si (100) wafers by varying their graphite concentration (nG) and thickness (t) from 2 to 12 wt% and 40 to 400 nm, respectively, in a RF sputtering system, subsequently annealed at 900 °C for 4 min, and then slowly cooled to room temperature to form graphene layers on Ni surfaces. Several structural-analysis techniques reveal the optimum nG (∼8 wt%) and t (∼160 nm) of the composite films for the synthesis of fewest-layer, defect-minimized graphene. At the annealing temperature, carbon atoms diffuse out from the composite film, followed by their precipitation as graphene on the Ni layer as the carbon solubility limit in Ni is reached during the cooling period. Based on this mechanism, the optimum conditions are explained. Our approach provides an advantage in that the number of layers can be simply tuned by varying nG and t of the composite films.