IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA10
Heteroepitaxy of a Manganese Carbonate on Calcite in Aqueous Solutions

Thursday, November 1, 2001, 5:00 pm, Room 122

Session: Nucleation & Growth
Presenter: A.S. Lea, Pacific Northwest National Laboratory
Authors: A.S. Lea, Pacific Northwest National Laboratory
A. El-Azab, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
J.E. Amonette, Pacific Northwest National Laboratory
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Heteroepitaxy of a manganese carbonate phase on the (1014) surface of calcite using an AFM has been observed in solution when the ion activity product of Mn@super 2+@ and CO@sub 3@@super 2-@ exceeds the solubility limit of MnCO@sub 3@. Thermodynamic data indicates that the resulting phase is a Mn@sub 0.5@Ca@sub 0.5@CO@sub 3@ phase and is consistent with our XPS and EPR measurements. These islands, while growing many microns in length along the [221] direction, have a uniform width of 150-220 nm and a uniform height of only 2.5 nm, corresponding to eight atomic layers. The islands cease growing when they encounter a step edge and have been observed to dissolve when undercut by a growing etch pit. Comparison of the crystal lattices of calcite and the Mn@sub 0.5@Ca@sub 0.5@CO@sub 3@ phase, indicate the direction of preferred growth is along the direction of greatest lattice mismatch, 3.3% as opposed to a mismatch of 2.2% along the direction of island width, [010]. A 25% decrease in stiffness along the [221] direction compared to the stiffness along the [010] direction is sufficient to account for this discrepancy. We have used a glued wetting layer model with conditions of constant surface chemical potential to model the observed morphology of the heteroepitaxial layer. Although not all the required parameters are accurately known, the model accurately depicts the measured cross-sectional profiles of the islands. This result implies that the models and considerations associated with nano-phase formation on surfaces in vacuum apply to a significant degree to growth in solution. @FootnoteText@ Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RL0 1830.