Compared optical properties of noble and transition metal-dielectric granular films

Metal-dielectric inhomogeneous media exhibit contrasted physical properties according to the nature of the metallic inclusion : noble or transition. A comparison between Au-MgO and Pt-Al2O3 thin films (prepared by sputtering), based on their optical, electrical and structural properties, is presented. The optical properties are analysed using two effective medium theories : Maxwell Garnett and Bruggeman. Both systems percolate at high metal volume fraction (0.4-0.5). They mainly differ in the dielectric anomaly and the influence of the conduction electron relaxation time on the optical properties of the inhomogeneous medium.