Plasmon Hybridization of the Concentric Aluminum Ring/Disk Nanocavities

The extinction spectra and electric field distributions of the aluminum nanoring and nanocavity structures consisting of a concentric disk and a surrounding ring (CDSR) covered by the oxide layer are calculated using the discrete dipole approximation method. The nanoring structures have much stronger electric field and much larger enhanced electric field region than those of the individual disk structure. The plasmon resonance modes of the CDSR nanocavity can be comprehended by the plasmon hybridization, which is coupled by the dipolar resonance mode of the individual disk and the antibonding, bonding dipolar resonance modes of the nanoring. The enhanced electric field distributions corresponding to the super-radiant and sub-radiant plasmon resonance modes of the CDSR nanocavity illustrate that the much stronger enhanced electric fields appear on the nanoring structure’s outer surface and the gap between the inner surface and the inserted disk for sub-radiant plasmon resonance mode, while for the super-radiant plasmon resonance mode, the much stronger enhanced electric fields only appear in the gap between the inner surface and the inserted disk. The maximum intensity reaches ~106 because of the dipolar resonance mode hybridization effect. The positions of the plasmon peaks depend sensitively on the nanostructural parameters. The plasmon resonance peaks of the CDSR nanostructure can be tuned throughout the visible and near-infrared regions by changing the size of nanostructures. Therefore, the properties of the tunable plasmon resonance modes, the much stronger and much larger region electric fields, make the aluminum CDSR nanocavity become a significant potential substrate for biological sensing, molecular detection, and the surface-enhanced Raman scattering.