Robust visibility of graphene monolayer on patterned plasmonic substrates.

Single and few-layer graphene flakes, while visible on a dielectric surface with customized thickness, cannot be optically imaged when exfoliated directly on semiconductors or metal substrates with arbitrary thickness. In this paper, we show that such graphene flakes become visible through a conventional microscope on a substrate patterned with a submicron sized, hexagonally packed array of gold disks. The interaction of the metal pattern with the incident light generates surface plasmon polaritons (SPPs) and results in enhanced reflectivity for certain angles and wavelengths. In the areas where graphene flakes are present, the interaction of the SPP with incident radiation is altered and consequently decreases the reflectivity in this region and increases the contrast, which accounts for the visibility of the graphene flakes on such substrates. We validate the observed contrast in visibility utilizing an in-house developed modified form of rigorous coupled wave analysis algorithm to appropriately incorporate the optical properties of two-dimensional materials. We present a parametric study of the contrast of graphene flakes on the patterned substrate to demonstrate the robustness of the visibility.