tunability of multipolar plasmon resonances and fano resonances in bimetallic nanoshells

We study the multipolar surface plasmon modes and its link to fano resonances in bimetallic nanoparticles. general expressions for the multipolar surface plasmon frequencies and damping rates are analytically derived by long-wave approximation. the results are in agreement with that from plasmon hybridization model for nanoshell system. numerical results show that the surface plasmon resonances and damping rates for au/ag and ag/au nanoshells exhibit quite different behavior with the increase of shell thickness. in addition, both the near-field diagram and the far-field quantity are theoretically investigated. fano resonances of scattering efficiency by ag/au core-shell nanoparticles occur due to the dipole-dipole coupling. the asymmetry of fano profiles can be tuned by adjusting the size ratio of the core and the shell. our results found some potential applications in optical devices and biomedicine.