X-ray scattering from surfaces of organic crystals

X-ray scattering experiments have been performed on the surfaces of organic crystals. The (010) cleavage planes of beta-alanine and alpha-glycine were investigated, and both specular and off-specular crystal truncation rods were measured. This allowed a determination of the molecular layering at the cleavage planes. Furthermore, the surfaces were investigated during growth and dissolution. No change in surface structure was observed, suggesting that the growth and dissolution is performed via the step edges. Finally, experiments on stereospecific adsorption of methionine on alpha-glycine were performed, showing that the (S)-methionine molecules are orderly attached to the (0 (1) over bar 0) surface of alpha-glycine and also attached to the (010) surface, but not in registry with the substrate.