Spectral Tuning of High Order Plasmonic Resonances in Multimodal Film‐Coupled Crystalline Cavities

Abstract Sub‐micrometric and ultrathin gold cavities sustain several high order planar plasmon resonances in the visible to near‐infrared spectral window that open new perspectives for the realization of self‐assembled metasurfaces or integrated components for nano‐optics. This article investigates in detail the far‐field spectral features of these multimodal crystalline gold nanoprisms, deposited on either dielectric (glass) or metallic substrates (Au, Al) by dark‐field scattering spectroscopy. Relying on the computation of the plasmonic density of states, the signature of each planar resonance is de‐convoluted from the experimental global response of single cavities as a function of the cavity size and the substrate nature. The redshifting dispersion of each resonance is extracted from this decomposition analysis and agrees with predictions from a Green dyadic method based numerical tool. In addition, in the presence of a metallic film, a characteristic redshift or blueshift of the global response is observed for each cavity that results from a metal‐specific redistribution of the resonances. The fine spectral tuning of high order plasmonic resonances achieved here reveals the potential of the metal–insulator–metal gap geometry for a static modal engineering within ultrathin gold cavities.