Tunable Fano Resonances in Three-Layered Bimetallic Au and Ag Nanoshell

The plasmon coupling in a three-layered Au/SiO2/Ag nanoshell has been investigated by means of Mie scattering theory. The dipole-dipole and dipole-quadrupole, Fano resonances have been observed in the extinction spectra of Au/SiO2/Ag nanoshells. With increase of the thickness of the middle layer, the dipole-dipole Fano resonance shows a blue shift and the magnitude of this Fano profile enhances while the dipole-quadrupole Fano resonance shows a red shift and reduces. With increase of the thickness of the outer shell, the dipole-dipole Fano minimum shows a blue shift and its magnitude decreases while both the energy and magnitude of dipole-quadrupole Fano resonance increase. All of the behaviors have been discussed with the plasmon hybridization model. In addition, the Au/SiO2/Ag nanoshell is found to show strong near-field enhancements in several regions, especially in the infrared region, which may provide effective applications in surface enhanced spectroscopy.