Controlling the density of pinhole defects in monolayer graphene synthesized via chemical vapor deposition on copper

The chemical vapor deposition of monolayer graphene on metal foils and thin films typically yields graphene that appears to be continuous and complete but that actually contains a high density of pinhole defects. These pinhole defects can be present at densities greater than 1 μm−2 and are problematic for many applications, ranging from the implementation of graphene in electronics to its use as a diffusion barrier. Here, we characterize pinhole defects in graphene films that are grown on Cu foils and epitaxial Cu thin films using CH4 as the precursor. On Cu foils, a relationship between surface roughness and the pinhole defect density is observed. A reduction in pinholes by a factor of ∼40 is realized by decreasing the foil surface roughness via increasing the annealing temperature and duration. The pinhole density is further reduced by a factor of ∼200 by using smoother epitaxial Cu thin films and additionally by extending the growth duration past the point of visual completion, as characterized by scanning electron microscopy. This study is expected to serve as a foundation for developing high quality substrates for graphene synthesis and realizing pinhole-free graphene.