Electromagnetic field redistribution in coupled plasmonic nanoparticle dimer-dielectric substrate system

Combining simulations and experiments, we demonstrate that the surface enhanced Raman scattering (SERS) system of a metal nanoparticle dimer on a dielectric substrate shows strong electromagnetic field enhancement in the particle/substrate gap because of the electromagnetic field redistribution. Besides, in some configurations, the presence of the substrate makes the strongest field enhancement in the gap between the two nanoparticles (i.e. the dimer) occur at the quadruple resonance, not the dipole resonance as usual. The result is very instructive in the difference between the ideal theoretical systems and the real experimental configuration.