Evolution of Strain in Heteroepitaxial Cadmium Carbonate Overgrowths on Dolomite

The evolution and accommodation of lattice strain in an epitaxial mineral film grown on an isostructural substrate were observed as a function of film thickness. Cadmium carbonate films (approximately CdCO3 (otavite) in composition) were grown on the (104) surface of CaMg(CO3)2 (dolomite) from aqueous solutions that were supersaturated with respect to both pure otavite and Cd-rich (Cd1–xCax)CO3. Specular and nonspecular X-ray reflectivity (XR) revealed that the structure and strain of the otavite overgrowths evolved in a manner that is fully consistent with a Stranski-Krastanov growth mode. Otavite films initially grew as coherently strained films, up to an average thickness of ∼15 A, with lateral compressive strains and an expansion of the vertical film lattice spacing resulting in a unit cell volume consistent with pure otavite. Thicker films (>15 A) became incommensurate with the substrate, having lattice parameters that are indistinguishable from pure otavite. These results indicate that the evolution...