Nanostructures for enhancing the SERS signal of a graphene monolayer in water and visible light absorption in a graphene monolayer

We numerically design and experimentally test a SERS-active substrate for enhancing the SERS signal of a monolayer of graphene in water. The monolayer is placed on top of an array of silver-covered nanoholes in a polymer and is covered with water. Here we report a large enhancement of up to 200000 in the SERS signal of the graphene monolayer on the patterned plasmonic nanostructure for a 532 nm excitation laser wavelength. Our numerical calculations of both the excitation field and the emission rate enhancements support the experimental results. We also propose a highly compact structure for near total light absorption in a monolayer of graphene in the visible. The structure consists of a grating slab covered with the graphene monolayer. The grating slab is separated from a metallic back reflector by a dielectric spacer. The proposed structure could find applications in the design of efficient nanoscale visible-light photodetectors and modulators.