Infrared Absorption of Nanocermets Close to the Percolation Threshold

(Received 6 May 1996, accepted 22 October 1996)

Abstract
We present a two dimensional simulation of the optical absorption of gold granular films, using a real space renormalization procedure. This numerical effective medium theory takes into account the actual morphology of the films. The results are compared both with experimental measurements and with other theoretical predictions asserting that the optical properties around the percolation threshold cannot be described by an effective dielectric function. Nevertheless, we obtain good agreement between the simulations and the experimental data, whatever the morphology and the concentration. It is concluded that the IR absorption can be attributed to the classical surface plasmon modes, generally situated in the visible spectral range for spheroidal inclusions, broadened here towards higher wavelengths due to the formation of fractal clusters of various sizes.