Robust Charge Transfer Plasmons in Metallic Particle–Film Systems

Understanding how the plasmonic response of a metallic nanoparticle is modified by its coupling with a metallic film is a fundamental research problem relevant for many applications including sensing, solar energy harvesting, spectroscopy, and photochemistry. Despite significant research effort on this topic, the nature of the interaction between colloidal nanoparticles and metallic films is not fully understood. Here, we investigate, both experimentally and theoretically, the optical response of surface ligand-coated gold nanorods interacting with gold films. We find that the scattering cross section of these systems is dominated by a charge transfer plasmon mode, for which charge flows between the particle and the film. The properties of this mode are dictated by the characteristics of the particle–film junction, which makes the frequency of this charge transfer plasmon far less sensitive to the nanoparticle size and geometry than a typical dipolar plasmon mode excited in similar nanorods placed directly on a purely dielectric substrate. The results of this work serve to advance our understanding of the interaction between metallic nanoparticles and metallic films, as well as provide a method for creating more robust plasmonic platforms that are less affected by changes in the size of individual nanoparticles.