Engineering Near-Field SEIRA Enhancements in Plasmonic Resonators

Engineering of the optical resonances in plasmonic resonator arrays is achieved by virtue of the intrinsic properties of the constituent structures such as composition, size, and shape and by controlling the inter-resonator interactions by virtue of the array's geometrical arrangement. The nanoscale confinement of the plasmonic field enhances light matter interactions, enabling, for instance, the surface-enhanced infrared absorption (SEIRA) effect. However, the subwavelength confinement also poses an experimental challenge for discriminating the response stemming from the individual resonators and from the collective response in densely packed arrays. In this work, the photothermal induced resonance technique is leveraged to obtain nanoscale images and spectra of near-field SEIRA hot spots observed in isolated plasmonic resonators of different shapes and in selected resonators within closely packed plasmonic arrays, informing on whether the interactions with neighboring resonators are beneficial or otherwise. Results are correlated with far-field spectra and theoretical calculations.