Electron Energy Loss Spectroscopy of Surface Plasmon Resonances on Aberrant Gold Nanostructures

Effects of structural elongation, annulation, and irregularity on emergent plasmonic modes were examined computationally and experimentally using low-loss electron energy loss spectroscopy (EELS). Resonant eigenstates were compared for multiple gold nanodisc shapes: circular, elongated, annulated, and acircular annulated. Losses of resonant eigenstates were mapped to distinguish discrete bright and dark resonance modes that emerged from morphological changes. Single bright and dark resonances exhibited by circular nanodiscs were supplemented by additional bright modes arising from axial asymmetry induced by radial aberrations in elongated discs. An antibonding bright mode appeared in annulated discs due to different dipole patterns arising from charge interactions on adjacent surfaces. Eccentricity on annulated discs hybridized resonant mode structures from discs, rings, and ellipses. Direct comparison between experimental measures and theory for a fabricated elongated nanoring with morphological distortions showed in vacuo discrete modes collapse into singular, red-shifted resonances with expanded bandwidths due to screening and interfacial damping with dielectric substrate and metallic adhesion interlayer. These results indicate effects of morphological aberrations and irregularities on the plasmon activity of deposited, self-assembled, and/or oxidized noble metal discs that may appear in natural environments.