Direct visualization of large-area graphene domains and boundaries by optical birefringency

The boundaries between domains in single-layer graphene(1-4) strongly influence its electronic properties(5-12). However, existing approaches for domain visualization, which are based on microscopy and spectroscopy(2,12-16), are only effective for domains that are less than a few micrometres in size. Here, we report a simple method for the visualization of arbitrarily large graphene domains by imaging the birefringence of a graphene surface covered with nematic liquid crystals. The method relies on a correspondence between the orientation of the liquid crystals and that of the underlying graphene, which we use to determine the boundaries of macroscopic domains.