Control of crystal nucleation by patterned self-assembled monolayers

An important requirement in the fabrication of advanced inorganic materials, such as ceramics and semiconductors, is control over crystallization(1-4). In principle, the synthetic growth of crystals can be guided by molecular recognition at interfaces(5-16). But it remains a practical challenge to control simultaneously the density and pattern of nucleation events, and the sizes and orientations of the growing crystals. Here we report a route to crystal formation, using micropatterned self-assembled monolayers(17,18), which affords control over all these parameters. We begin with a metal substrate patterned with a self-assembled monolayer having areas of different nucleating activity-in this case, an array of acid-terminated regions separated by methyl-terminated regions. By immersing the patterned substrates in a calcium chloride solution and exposing them to carbon dioxide, we achieve ordered crystallization of calcite in the polar regions, where the rate of nucleation is fastest; crystallization can be completely suppressed elsewhere by a suitable choice of array spacing, which ensures that the solution is undersaturated in the methyl-terminated regions. The nucleation density (the number of crystals formed per active site) maybe controlled by varying the area and distribution of the polar regions, and we can manipulate the crystallographic orientation by using different functional groups and substrates.