Plasmonic Phenomena in Metallic Nanocap

The optical properties of the composite nanostructure based on the spherical dielectric particle incompletely covered by the metallic shell (nanocap) have been investigated. The expressions for the diagonal components of the polarizability tensor, absorption, scattering and extinction cross-sections, and radiation efficiency are obtained. The methodology for determining the transverse and longitudinal effective relaxation rates is proposed. The frequencies of the transverse and longitudinal surface plasmonic resonances are obtained within the framework of the hybridization of the modes of the elementary (simplest) forms of the plasmonic nanostructures – the metallic segment and the dielectric cavity in metal. The frequency dependences of the real and imaginary parts, as well as the modulus of the diagonal components of the polarizability tensor, absorption, scattering and extinction cross-sections, and radiation efficiency have been calculated. The qualitative similarity and quantitative proximity of the corresponding curves for the transverse and longitudinal polarizabilities have been established. It is shown that the amplitude, spectral position and number of maxima of the absorption, scattering and extinction cross-sections essentially depend on the geometrical parameters of the nanostructure, and the maxima at some resonance frequencies are not visually observed due to the smallness of their amplitude. The influence of the geometrical parameters, core and shell material properties on the position and amplitude of the maxima of the extinction cross-section is investigated. The simpler scheme of the hybridization of the plasmonic modes, based on the Drude model, conditions of the absence of the energy losses and excitation of the transverse and longitudinal plasmonic surface resonances, is developed. This scheme differs from the scheme, which is used in the number of the known works. An increase in the splitting of the longitudinal and transverse surface plasmonic resonances with increasing volume content of the dielectric in the nanostructure is proved. The growth of the radiation efficiency of the nanostructures, which are under the study, with increasing content of the metallic fraction in them is demonstrated.