Large-scale sub-100 nm compound plasmonic grating arrays to control the interaction between localized and propagating plasmons

Abstract

Compound plasmonic resonances arise due to the interaction between discrete and continuous metallic nanostructures. Such combined nanostructures provide a versatility and tunability beyond that of most other metallic nanostructures. In order to observe such resonances and their tunability, multiple nanostructure arrays composed of periodic metallic gratings of varying width and an underlying metallic film should be studied. Large-area compound plasmonic structures composed of various Au grating arrays with sub-100 nm features spaced nanometers above an Au film were fabricated using extreme ultraviolet interference lithography. Reflection spectra, via both numerical simulations and experimental measurements over a wide range of incidence angles and excitation wavelengths, show the existence of not only the usual propagating and localized plasmon resonances, but also compound plasmonic resonances. These resonances exhibit not only propagative features, but also a spectral evolution with varying grating width. Additionally, a reduction of the width of the grating elements results in coupling with the localized dipolar resonance of the grating elements and thus plasmon hybridization. This newly acquired perspective on the various interactions present in such a plasmonic system will aid in an increased understanding of the mechanisms at play when designing plasmonic structures composed of both discrete and continuous elements.