Ultrathin layers of gold, from 2 to 25 nm of nominal coverage, have been deposited on sodium-alginate biopolymer foils applying two alternative approaches: low power sputtering and thermal evaporation. The morphology of the deposited layers was obtained by means of atomic force microscopy. In the early stages of growth, thermal evaporation gives rise to a top surface resembling the underlying substrate, whereas low power sputtering produces a topography characterized by smoother areas. This indicates that the film growth occurs in different ways. X-ray photoelectron spectroscopy with two photon energies, corresponding to Al Kα and Ag Lα photons, was used to get information on the chemistry at the interface and on the degree of intermixing between Au and sodium-alginate. While no chemical modifications with respect to the bare materials could be detected, the evolution of the intensities of the relevant …