Grain and void resonances in granular silver films near the percolation threshold: Experiment and simulation using an entropic model

Granular metal films with low metal fractions exhibit the well-known resona nt absorption, due to the excitation of surface plasmons in the metallic gr ains, that is not satisfactorily described by the effective medium theories (EMT) close to the percolation threshold. We have recently developed an op tical model, which is based on the entropic analysis in the actual image of a heterogeneous medium. This model accounts well for the optical propertie s of silver granular films around the percolation threshold. In addition to the so-called plasmon resonant absorption, the model predicts a weak absor ption, on the edge of the main one, which we attribute to the dielectric vo id resonance. Both absorptions are effectively observed in granular films c lose to the percolation threshold. Our model gives a fair account of the po sition of these two resonant absorptions and of their variation when the in dex of the dielectric medium is experimentally changed by embedding the fil m in a glycerin layer. (C) 2000 Elsevier Science B.V. All rights reserved.