The scattering of high-energy electrons. II. Quantitative validity domains of the single-scattering approximations for organic crystals

Two approximations that are commonly used to describe the scattering of high-energy electrons are the first Born approximation (kinematic approximation) and the closely related 'weak phase-object' approximation. The quantitative domains of validity for the use of these two scattering approximations for structural analysis of organic crystals are evaluated numerically in terms of resolution, crystal thickness and incident electron energy. The resulting calculations show how progressively important dynamical scattering effects lead to an increasingly large contribution to the R value in a structure factor analysis. Alternatively, the results show that an increasing dissimilarity is produced between the structure inferred from electron microscope images and the correct structure. The results also show that the actual images (and the structure inferred from the images) remain qualitatively similar to the projected Coulomb potential, even though dynamical scattering effects may lead to a large quantitative dissimilarity relative to the correct structure.