ANOMALOUS INFRARED-ABSORPTION OF NANOCERMETS IN THE PERCOLATION RANGE

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. Results are compared both with experimental measur ements and with other theoretical predictions asserting that the optic al properties around the percolation threshold cannot be described by an effective dielectric function. Nevertheless. we obtain a good agree ment between simulations and experimental data, whatever the morpholog y and the concentration, it is concluded on both theoretical and exper imental arguments that the LR absorption can be attributed to classica l surface plasmon modes, generally situated in the visible spectral ra nge for spheroidal inclusions, broadened here towards higher wavelengt hs due to the formation of fractal clusters of various sizes and shape s.