Transmission of visible light through oxidized copper films: feasibility of using a spectral projected gradient method.

Transmittance measurements at normal incidence were carried out over the visible spectral range for metallic thin films deposited by electron beam evaporation on thick glass substrates. The presence of an inhomogeneous thin layer of Cu2O covering the deposited Cu films is required for a satisfactory model of the measurements taken from various samples with increasing thickness. A spectral projected gradient method is used to invert the transmission spectra from which the wavelength dependence of the effective dielectric function of the oxidized coating layer is obtained. Then an effective medium model is used to estimate the volume fraction of internal voids randomly distributed through the surface layer.