The correction of geometrical factors in the analysis of X-ray reflectivity

X-ray reflectivity is a powerful technique to study electron density profiles in the direction normal to the surface of a fiat sample. As usual in scattering experiments, where the phase information is lost, it is necessary to build a model that can be used to calculate the reflectivity for comparison with the measured reflectivity. In the calculations, it is necessary to correct the calculated reflectivity from geometrical and resolution-function factors, which play a major role at low angles of incidence. These factors are presented in this paper and the corrected calculated intensity is compared with the measured reflectivity of a commercial silicon wafer and of a niobium film on a sapphire substrate.