Theoretical Study of Sensitivity and Localized Surface Plasmon Resonance of Ag-Dielectric Core-Shell Multi-layered Nanosphere

Abstract

Localized surface plasmon resonances (LSPRs) of Ag-dielectric-Ag multi-layered nanoshell are studied by quasi-static approximation and plasmon hybridization theory. Absorption properties of multi-layered nanoshell with the silver core and nanoshell separated by a dielectric layer exhibit strong coupling between the core and nanoshell. The result shows absorption spectrum of LSPRS is influenced by the refractive index of surrounding medium, the dielectric constant of middle dielectric layer, the thickness of inner core radius and outer shell layer. LSPR shift of the longest wavelength $\left |\omega _{-}^{-}\right >$ is red-shifted with increasing the inner core radius. It is interesting to find that longer wavelength $\left |\omega _{-}^{+}\right >$ mode is mainly effected by the ratio constant of the surrounding medium refractive index ε ₄ to the middle layer dielectric constant ε ₂. $\left |\omega _{-}^{+}\right >$ mode takes place a blue-shift with increasing inner core radius when ε ₂ > ε ₄, a red-shift when ε ₂ < ε ₄, and no-shifting when ε ₂ = ε ₄. However, the influence of dielectric layer radius to $\left |\omega _{-}^{+}\right >$ mode shows the different property as that of increasing the inner core radius. The underlying mechanisms are analyzed with the plasmon hybridization theory and the distribution of induced charge interaction between the inner core and outer shell. In addition, the influence of core radius, middle dielectric layer radius and outer shell radius to sensitivity of Ag-dielectric-Ag multi-layered nanoshell are also reported, a higher sensitivity could be gotten by adjusting geometrical parameters. Our theoretical study could give an easy way to analyze properties of the core-shell nanosphere based on plasmon hybridization theory and the induced charge interaction, and usefully broaden the applications in nano-optics.