Chemical Vapor-Deposited Graphene on Ultraflat Copper Foils for van der Waals Hetero-Assembly.

The purity and morphology of the copper surface is important for the synthesis of high-quality, large-grained graphene by chemical vapor deposition. We find that atomically smooth copper foils-fabricated by physical vapor deposition and subsequent electroplating of copper on silicon wafer templates-exhibit strongly reduced surface roughness after the annealing of the copper catalyst, and correspondingly lower nucleation and defect density of the graphene film, when compared to commercial cold-rolled copper foils. The "ultrafoils"-ultraflat foils-facilitate easier dry pickup and encapsulation of graphene by hexagonal boron nitride, which we believe is due to the lower roughness of the catalyst surface promoting a conformal interface and subsequent stronger van der Waals adhesion between graphene and hexagonal boron nitride.