FACET MORPHOLOGY RESPONSE TO NONUNIFORMITIES IN NUTRIENT AND IMPURITYSUPPLY .1. EXPERIMENTS AND INTERPRETATION

The growth morphology and kinetics of crystal facets were investigated by in-situ high-resolution optical interferometry, using tetragonal l ysozyme as a model system. The protein composition of the growth solut ions was characterized by high pressure liquid chromatography and gel electrophoresis. In relatively pure solutions, the facets exhibited de pressions with lower vicinal slope at their edges. In solutions with l ess than or equal to 1% of protein impurities, that were found to be i ncorporated into the crystal, the depressions in the facets had higher vicinal slope at the edges. These deviations from planarity increased with crystal size and growth rate. This indicates that transport-indu ced nonuniformities in the nutrient and impurity concentrations cause these microscopic shapes. Quantitative accounts of both interface shap es are possible only if one assumes strong overlap of the coupled volu me and surface diffusion fields of growth steps. From this we conclude that the characteristic surface diffusion length of ad-molecules on l ysozyme {110} facets is of order 1 mu m or similar to 200 molecule dia meters. The values obtained for the average step (tangential) velociti es in the lower purity solutions suggest that the impurities affect gr owth kinetics through their adsorption at kink sites.