Effect of substrate on the properties of localized surface plasmon

Abstract

Metallic nanostructures have great potential for bio-chemical sensor applications due to the excitation of localized surface plasmon and its sensitive response to environmental change. The optical properties of the localized surface plasmon strongly depend on the size, shape, metal composition, and the local environment. The properties are influenced by the substrate that supports the metallic nanostructure, as well. The substrate materials can be classified into the transparent dielectric, the absorptive semiconductor, and the reflective metal. The materials selection for the substrate has been reported to have an effect in a different way on the plasmonic properties of metal nanostructure supported on it. Unlike the dielectric, it has been known that the semiconductor induces a damping of plasmon due to the energy loss by absorption, and the metal substrates give rise to an additional hybridized mode from the interaction with the free electrons on the metal surface. We investigate the effect of substrate more systematically by controlling the extent that the local electric field of metal nanostructure feels the substrate, which can be modified by the orientational relation with the light polarization, the distance to the substrate, and the decay length of metal nanostructure itself. The optical scattering was analyzed as a function of the key controlling factor mentioned above using a dark field spectroscopy. Theoretical electrodynamic calculations were also carried out and compared with the experimental results. Grant from Center for Nanostructured Materials Technology (2009K000459)