(250a) Mass Transport Limitations During AFM Measurements of Crystal Growth From Solutions

Authors: 
Wang, W., University of Minnesota
Yeckel, A., University of Minnesota
Derby, J. J., University of Minnesota


Atomic force microscopy (AFM) fluid cell has become a prominent experimental tool for in situ measurements of crystal faces growing from solution phase.  This technique has been used to investigate micro-scale features of solution crystal growth of various organic and inorganic crystals, including imaging of terraces, ledges, and kinks, and the direct measurement of kink and step velocities.  These measurements permit estimates of thermodynamic and kinetic properties of solution crystal growth.  However, the crystallization conditions present in the AFM fluid cell are typically not well understood.  Of special importance are mass transport limitations caused by crystal growth and the effect of flows through the AFM system.

Using a parallel, finite element model validated in prior work, we present detailed, three-dimensional computations of fluid flow and mass transfer through an AFM fluid cell to access the parametric sensitivity of growth conditions to factors such as the strength of flow, the direction and frequency of scanner motion, the size of the crystal, the kinetics of the growing surface, and the geometry of the AFM cantilever.

Of special importance in this presentation, we describe a simplified, two-dimensional analytical model that focuses on the area near the growing crystal surface and the AFM cantilever.  This model was based on the insight obtained from the three-dimensional model.  The two-dimensional model promises to serve as a more general tool that may be applied to many AFM crystal growth systems to correlate behavior, without the need for the detailed numerical modeling approach we originally employed.  Accounting for such effects will be very important to faithfully interpret AFM measurements of growth dynamics.

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