Ellipsoidal core-shell dielectric-gold nanostructure: Theoretical study of the tunable surface plasmon resonance

The dependence of surface plasmon resonance (SPR) characters of core-shell structure ellipsoidal nanorods was investigated as functions of the gold shell width and dielectric constant. A dipole-limit calculation indicated that, there are four SPR absorption peaks occur. The two shorter wavelength peaks are attributed to the transverse resonances, whereas the two longer wavelength peaks are attributed to the longitudinal resonances. Both transverse and longitudinal resonances are split into inner surface and outer surface modes, respectively. When the core size is a fixed value, the two transverse surface plasmon peaks red shift as the gold shell width is increased. On the other hand, both the inner and outer surface modes attributed to the longitudinal surface plasmon peaks blue shifts distinctly and nonlinearly. Further more, both the inner and outer surface plasmon modes are also dependent on the embedding medium and core dielectric constant. The longitudinal SPR from inner surface is more sensitive to the core dielectric constant, whereas the longitudinal SPR from outer surface is more sensitive to the surrounding medium.