Crystallization of malonic and succinic acids on SAMs: toward the general mechanism of oriented nucleation on organic monolayers.

Self-assembled monolayers (SAMs) were shown to induce very specific oriented growth of simple organic and inorganic crystals. Here we present a detailed study of the mechanism by which SAMs control the oriented nucleation by examining a more complex case of crystallization of bifunctional organic molecules. Malonic and succinic acids were grown on the SAMs of HS(CH(2))(10)CO(2)H and HS(CH(2))(11)CO(2)H supported on gold films. Each SAM induced a very controlled, specific orientation of the crystals. The preferred nucleating planes always exhibited an alignment of one of the carboxylic acid groups in the molecules of the growing crystal with the carboxylic acid groups on the surface of the SAMs. These results suggest that the translation of the structural information through the interface occurs by stereochemical registry such that the functional groups in the SAM play the role of an oriented surrogate layer for the nucleating crystal. These findings are very important to the understanding of the underlying principles by which various organic surfaces-and most probably also biological templates-control the crystallization process.