Calcite Crystallization on Polarized Single Calcite Crystal Substrates in the Presence of Poly-Lysine

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We demonstrated the crystallization of calcite on nonpolarized and polarized (10.4)-oriented calcite single crystal substrates in the presence of poly-lysine (PLys) as a poly amino acid. The PLys and the electric field due to polarized calcite substrates showed a significant effect on the morphologies of calcite precipitates. At a small amount of PLys, rhombohedral calcite crystals, with notches in the edges of the rhombohedra, formed through homoepitaxy and constructed aggregates with an island structure. At a large amount of PLys, the calcite precipitates had overgrown calcite crystals, which were formed by epitaxial growth on each of the rhombohedral surfaces of already formed calcite rhombohedra, and the calcite aggregates became elongated in the direction perpendicular to the substrate. As the amount of PLys increased, the overgrown calcite crystals tapered toward their ends, and some of the overgrown calcite crystals exhibited a cone-shaped appearance. These cone-shaped crystals consisted of aggregates with a needle-like morphology. The PLys addition and the electric fields due to the polarized calcite substrates on calcite crystallization were apparent most remarkably on a negatively charged surface of these substrates. We proposed the formation mechanism of calcite precipitates on the oriented calcite substrates in the presence of PLys.