X-ray, electron and neutron scattering techniques have been used for the structural characterization of surfaces and embedded morphologies. Several theories have been developed to explain the scattering phenomena including modified Distorted Wave Born Approximations (DWBA), the Phase-Object Approximation (POA) [1] and, for periodic structures, a Dynamical Theory (DT) [2]. It has been shown that these theories have some limits of applicability in x-ray and electron scattering measurements. The aim of the proposal is to determine by comparsion of theoretical expectation and measurements the regions of validity of the theories.