Fig. 1
Schematic of metamaterials for multiband and broadband absorption enhancement of graphene at optical frequencies, which are composed of a graphene monolayer sandwiched between four Ag nanodisks and a SiO2 spacer on an Ag substrate. Geometrical parameters p x and p y are the array periods along the x and y directions, respectively; t is the thickness of the SiO2 spacer; d 1 , d 2 , d 3 , and d 4 are the diameters of four Ag nanodisks (d 1 > d 2 > d 3 > d 4 ); h is the height of the Ag nanodisks. Ein, Hin, and Kin are the electric field, magnetic field, and wave vector of the incident light, which are along the x, y, and z axes, respectively