The reflectance spectroscopy of silver surface layers on gold and aluminium substrates

The results of reflectivity and differential reflectivity measurements at non-normal incidence for p-polarized light of thin films of silver on different substrates are presented. It was found that the peak associated with the silver plasma frequency broadens and shifts towards higher energies for thinner layers. A model of a thin layer with bulk silver optical constants cannot be used to explain this behaviour. Agreement with experiment is obtained if we take into account not only the shorter relaxation time of the free electrons but also the non-local effects associated with the longitudinal wave (polarization wave) near the plasma frequency (in our configuration these effects are particularly important).