Au@Ag core-shell nanoparticles: efficient all-plasmonic Fano-resonance generators.

Fano resonances (FR) in strongly coupled systems like a metallic dimer arise due to the coupling between the spectrally localized surface plasmon resonance (SPR) of a noble metal nanoparticle and the continuum of interband transitions of the other. Since its discovery in Au-Ag dimers, several plasmonic structures have been proposed as candidates for obtaining Fano resonances. However, most of them either are difficult to synthesize or do not generate FR signal of adequate intensity. In this paper we demonstrate that simple Au@Ag core-shell nanoparticles with typical shell thickness below 5.0 nm, which can be synthesized through a common citrate reduction method, have a Fano resonance easily detectable in the far-field.