Optical properties of electrically insulating granular metal films

By successive evaporation of metal and dielectric we have made films consisting of many layers of small metal particles insulated from each other. Such films are opaque in the visible and near infrared, but electrically insulating. We have measured the dependence of the optical properties on metal particle size and metal-to-insulator volume ratio. The results can be qualitatively understood in terms of the Maxwell-Garnett theory. Possible technical applications are discussed.