Plasmons are collective electron oscillations usually excited at metal surfaces by a light source. Doped graphene layers have also shown the similar surface plasmon effects to that of metallic thin films.[6][7] Through the engineering of metallic substrates or nanoparticles (e.g., gold, silver and copper) with graphene, the plasmonic properties of the hybrid structures could be tuned for improving the optoelectronic device performances.[8][9] It is worth noting that the electrons at the metallic structure could transfer to the graphene conduction band. This is attributed to the zero bandgap property of graphene nanosheet.

Graphene plasmons can also be decoupled from their environment and give rise to genuine Dirac plasmon at low-energy range where the wavelengths exceed the damping length. These graphene plasma resonances have been observed in the GHz–THz electronic domain.