Adjustable optical properties of coatings based on cermet thin films near the percolation threshold

The optical and electrical properties of metal-dielectric composites (cermets) show large variations as a function of volume fraction, size, shape and the statistical distribution of metallic grains in the dielectric. The flexibility of the optical properties around the percolation threshold can be used to develop new spectrally selective multilayer coatings consisting of a PtAl2O3 cermet absorbing film, an Al2O3 antireflecting film and an Al2O3 underlayer, deposited on a metallic substrate. These coatings are totally absorbing in the visible range and highly reflective in the IR, with an adjustable cutoff wavelength.