Anomalous dispersion of surface plasma oscillations*

We observed that a monomolecular layer of an organic dye strongly influences the surface plasma oscillation (SPO) on thin silver films in spectral regions where the dye absorbs. Experimentally, squarylium dye was deposited by the Langmuir-Blodgett monolayer technique and the silver-dye films were investigated by their SPO’s. Within the absorption band, the SPO’s exhibited an anomalous dispersion and a pronounced variation in the damping. To explain this behavior, theoretical model calculations and approximate expressions are presented which show the relationship between the dielectric function of the coating and the observed effect. The influence of anisotropy is briefly outlined.