Thin nickel films deposited by d.c. magnetron sputtering on glass substrates were thermally annealed in air at temperatures in the range of 380-530 degrees C. The annealed samples were analyzed by ex situ spectroscopic ellipsometry. X-ray diffraction data reveal that during the oxidation process only the Ni and NiO phases are present. Thus, using an appropriate model that describes the ellipsometric spectra, the thickness of the NiO layer was obtained as a function of annealing temperature with an activation energy of 1.74 eV. Furthermore, a parabolic kinetics was found for the NiO thickness dependence on annealing time. (c) 2005 Elsevier B.V. All rights reserved.