The results of spectral and angle-dependent ellipsometric measurements of r.f. magnetron-sputtered very thin nickel, molybdenum and nickel nitride films deposited onto [100] oriented silicon substrates have been reported. Ellipsometric data were taken over the spectral range of 348-806 nm. The parameters of the films, namely, film thicknesses and volume fractions for the constituents have been calculated from the ellipsometric data by the best fitting procedure using one-layer (air/Metal/Si), two-layer (air/Metal/SiO2/Si) and three-layer (air/Metal oxide/Metal/SiO2/Si) optical models. We have estimated the roughness on the film surfaces and contamination of the films by Si and SiO2 using the Maxwell-Garnett and Bruggeman effective medium approximations. We have also used a model with an inhomogeneous silicon dioxide interface (a mixture of SiO2 and a-Si). The ellipsometric measurements along with computer data processing will be useful for quality control during the manufacturing of the films, which have applications in soft X-roy optical systems.