Anomalies in the surface plasmon resonance excitation at both surfaces of evaporated metal films

Measurements of the resonant excitation of surface plasmons at both the air and substrate surfaces of evaporated Ag films indicate that the real part of εAg is a larger negative number at the substrate interface. This difference can be explained with a Maxwell-Garnett type theory which assumes that the film density near the air surface is several percent below that near the substrate interface.