Substrate effect on the optical response of silver nanoparticles

We study the influence of a substrate on the surface plasmon resonance absorption in silver nanoparticles depending on the distance between the nanoparticles and the substrate. The experimentally observed red shift of the resonant absorption is explained in the frame of the image-induced charges at the interface between the ambient medium and the substrate. The influence of a metallic substrate is negligible when the clusters are at a distanced d > 2R from the substrate. A dielectric substrate has much less influence on the optical response of silver clusters than a metallic one.