INFRARED-ABSORPTION OF NANOCERMETS CLOSE TO THE PERCOLATION-THRESHOLD

We present a two dimensional simulation of the optical absorption of g old granular films, using a real space renormalization procedure. This numerical effective medium theory takes into account the actual morph ology of the films. The results are compared both with experimental me asurements and with other theoretical predictions asserting that the o ptical properties around the percolation threshold cannot be described by an effective dielectric function. Nevertheless, are obtain good ag reement between the simulations and the experimental data, whatever th e morphology and the concentration. It is concluded that the IR absorp tion can be attributed to the classical surface plasmon modes, general ly situated in the visible spectral range for spheroidal inclusions, b roadened here towards higher wavelengths due to the formation of fract al clusters of various sizes.