A MICROSCOPIC THEORY OF THE REFLECTION PROPERTIES OF METAL-INSULATOR COMPOSITE FILMS

We present a microscopical approach for the reflectance of metal-insulator granular films. We incorporate in the theory the precise description of the geometrical properties of the metallic clusters as it is given by the scaling theory of percolation. We predict in particular the dependence of the reflectance with respect to the wavelength and to the concentration in the vicinity of and at the percolation threshold. Our theory predicts behaviors which strongly differ from those of effective medium theories. These results have been announced by us at the ETOPIM 2 congress. In this paper, we present the details of the calculations. We finally apply our theory to the case of the infrared properties of granular Au films; this analysis shows a good agreement of our theory with the experimental results in contrast to the effective medium theories.