Optical properties of Ag-SiO2Cermet films: A comparison of effective-medium theories

We analyze the optical transmittance of metal-rich Ag-Si${\mathrm{O}}_2$ cermet films, as measured by Cohen et al., in terms of several effective-medium theories. Taking one triplet of depolarization factors to characterize the Si${\mathrm{O}}_2$ inclusions we demonstrate that the experimental data fall in between the predictions of a formulation based on the Maxwell-Garnett theory and the self-consistent effective-medium theories founded on the works by Bruggeman, by Maxwell-Garnett in conjunction with Polder and van Santen, and by Hunderi. None of the self-consistent theories can be reconciled with the experimental finding of a transmittance minimum in the visible range, whereas such an effect can be accounted for, at least qualitatively, by incorporating a distribution of depolarization factors in the Maxwell-Garnett type formalism. We stress, however, that available experimental data are yet too sparse to permit any totally confident conclusions regarding the overall superiority of any particular effective-medium theory.