Plasmonic Nanopores in Metal-Insulator-Metal Films

A novel type of plasmonic nanopore array in a metal-insulator-metal thin film is presented. The optical properties of this structure are described using a generic theoretical framework for surface waves in a coupled multilayer system. The characteristic spacing (short-range order) of the pores enables grating-type coupling to hybridized surface plasmons, with stronger coupling to some modes than others. The nature of the optical resonances and their excitation mechanisms can be conceptually understood from a charge distribution argument. The experimental results are further verified by numerical simulations, which also enable visualization of the near field. This study illustrates the surface plasmon characteristics (sensitive to periodicity) of the extinction maximum in the asymmetric spectral resonance induced by aperture arrays, while the transmission maximum corresponds to a resonance of localized character (sensitive to pore shape). Finally, the use of these nanopores for sensing applications through changes in the refractive index is evaluated.