Geometry for Maximizing Localized Surface Plasmon Resonance of Au Nanorings with Random Orientations

The reduction of average extinction cross section of a localized surface plasmon (LSP) resonance mode under the random orientation condition of Au nanoring (NRI) distribution is first numerically demonstrated. The reduction range depends on the geometry symmetry property of the electron oscillation axis in the LSP resonance mode. Then, by increasing the ring height, an optimized Au NRI geometry is designed to make the resonance wavelengths of its cross-ring dipole mode and axial dipole mode the same. In such an Au NRI, a few higher-order axial LSP modes are discovered. Also, under the condition of random orientation distribution, the ranges of extinction, scattering, and absorption cross section reductions from the corresponding maximum levels of optimized excitations are significantly decreased, when compared with the counterparts of the Au NRIs of a smaller ring height.