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 px and py are the array periods along the x and y directions, respectively; t is the thickness of the SiO2 spacer; d1, d2, d3, and d4 are the diameters of four Ag nanodisks (d1 > d2 > d3 > d4); 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