Abstract

We study the properties of plasmonic excitations localized at 2D and 3D nanoscale perturbations of a flat metal surface within the general method of surface integral equations. The resonant values of the optical permittivity ${\epsilon }_j$ and the plasmonic eigenfunctions—distributions of the surface charge density ${\sigma }_j(\mathbf{r})$—are investigated. General symmetry properties linking the cases of convex and concave perturbations (bumps and mirror-reflected pits) are established. The impact of the height-to-width perturbation ratio $h_0/r_0$ on the localized surface plasmons is twofold: while the resonant permittivities ${\epsilon }_j$ drop linearly with $h_0/r_0$ leading to strong redshifts of the resonances, the scale of localization stays constant ($\approx r_0$). The presence of sharp shape features (tips and corners) with the curvature radius ${\rho }_0\ll r_0$ leads to superlocalization of charge density on the scale of ${\rho }_0$ and, simultaneously, to an additional strong drop of ${\epsilon }_j$.

© 2014 Optical Society of America

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