Recovering effective thicknesses and optical properties of copper and copper oxide layers from absorbance measurements
Nowadays, the recovering of both thicknesses and optical properties of nanometric multilayers is still a challenge. We propose a method to recover the effective relative permittivities and the thicknesses of copper/copper oxide layers, from absorbance spectra measured in the visible spectra. The experimental data are fitted with a model of classical light-matter interaction and a combination of two Drude-Lorentz laws to calculate the relative permittivities over the spectrum. The Particle Swarm Optimization and the evolutionary methods are used for the least-square fitting. A two steps study reveals that the relative permittivities of bulk cannot be used to fit adequately the absorbance curves. However, a perturbation of these reference values improves their fitting. The method is applied to the absorption spectra of a set of three copper samples that are progressively oxidized by six successive heat treatments.