Surface-to-volume ratio controls the radiation of stratified plasmonic antennas

Surface plasmons are excited at a metal/dielectric interface, through the coupling between conduction electrons and incident photons. The surface plasmon generation is therefore strongly determined by the accessibility of the surface to the incoming electromagnetic field. We demonstrate the role of this surface for plasmonic nanoantennas with identical volumes and resonant lengths. An antenna is stratified parallel to the plane of its main dipolar resonance axis and the influence of the number of layers and the spacing between them on the optical properties of the antenna are investigated experimentally. We show that increasing the number of layers and, hence, increasing the total accessible surface of the antenna, results in an enhanced scattering cross section and a redshift which indicates that lower energy photons are required to couple to the metal electrons. In particular, the far-field enhancement observed for double-layer nanostructures suggests that standard single-layer metal deposition can be easily and advantageously substituted with metal/dielectric/metal deposition to boost light scattered by a plasmonic antenna