Conductive Ag/Au Nanoparticle Films with Enhanced Second- Harmonic Generation Exceeding Percolating Limitation

Nonlinear optical signals of metallic nanoparticle films usually reach the maximum at the percolation threshold with a semicontinuous nanostructure due to the enhancement of the percolating effect. Here, we deposited Ag nanoparticles on the percolating Au nanoparticle film to construct conductive Ag/Au bilayer films and comparatively explored second harmonic generation (SHG) of single-component (Au or Ag) and two component Ag/Au nanoparticle films. Intriguingly, we observed a 680% SHG enhancement of the Ag/Au bilayer film compared to that of the percolating Au nanoparticle film, which is caused by a cooperative effect of surface plasmon resonances, interband transitions, and the percolation effect. These observations provide a strategy to design nonlinear photonic nanodevices with optimized nonlinear performance.