Corrections for surface X-ray diffraction measurements using the Z-axis geometry: finite size effects in direct and reciprocal space

X-ray diffraction data have to be corrected by geometrical correction facto rs prior to any quantitative analysis. Here the case of grazing incidence X -ray diffraction measurements is considered, including the case of high exi t angles. First, an approach taking into account the evolution of the diffr acting area during an ! scan is presented. From the calculation of the effe ctive part of the sample surface that participates in the diffraction pheno mena at each step of the scan, a more accurate correction factor than those commonly used is derived and the evolution of the line shape along a zero- width rod is explained. Secondly, the case of finite-width rods, under the point-like sample approximation, is considered: the influence of the partia l integration, as a result of the detector in-plane acceptance, of a rod wi th an anisotropic in-plane shape, is studied and leads to an analytical exp ression for the corresponding correction factor. Finally, a full numerical simulation is presented, which provides an alternative method for correctin g the experimental intensities and shows in which conditions the previous f ormulae are no longer valid.