Launching graphene surface plasmon waves with vanishingly small periodic grating structures.

Graphene is now a crucial component of many device designs in electronics and optics. Just like the noble metals, this single layer of carbon atoms in a honeycomb lattice can support surface plasmons, which are central to several sensing technologies in the mid-infrared regime. As with classical metal plasmons, periodic corrugations in the graphene sheet itself can be used to launch these surface waves; however, as graphene plasmons are tightly confined, the role of unwanted surface roughness, even at a nanometer scale, cannot be ignored. In this work, we revisit our previous numerical experiments on metal plasmons launched by vanishingly small grating structures, with the addition of graphene to the structure. These simulations are conducted with a recently devised, rapid, and robust high-order spectral scheme of the authors, and with it we carefully demonstrate how the plasmonic response of a perfectly flat sheet of graphene can be significantly altered with even a tiny corrugation (on the order of merely 5 nm). With these results, we demonstrate the primary importance of fabrication techniques that produce interfaces whose deviations from flat are on the order of angstroms.