Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation

Abstract

ABSTRACT:The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry and x-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ~1 s/frame, which is ~50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the Calcite (CaCO3) constitutes the largest carbon reservoir on Earth 1 and its dissolution plays a major role in the global carbon cycle in nature 2, 3 , as well as in technologies such as geologic CO2

Temporal Evolution of Calcite Surface Dissolution Kinetics

“…As mentioned above, detailed AFM studies of dissolving calcite have made critical advances in quantifying the dynamics of surface features at or close to the atomic scale [26,27], and have focused largely on step movement. The AFM studies conducted in situ have easily detailed the anisotropy in step velocities, quantifying the variation of crystallographically inequivalent "obtuse" 441 + , 481 + and "acute" 441 − , 481 − steps as a function of saturation state, impurity burden, pH, ionic strength, and other controls (work reviewed in ref.…”

Imaging the Solvation of a One‐Dimensional Solid on the Molecular Scale

“…[7][8][9] Atomic force microscopy experiments conducted in solution imaged the dissolution of solids on the nanometer scale. [10][11][12][13] However,a st hese experiments are conducted mostly under ambient conditions,t he interactions of individual solvent molecules with the solid are not traceable owing to intrinsic thermal fluctuations.Low-temperature scanning tunneling microscopy (STM) eliminates the thermal motion of molecules and offers the required spatial resolution. [14,15] Here,weused this technique to follow the solvation of ah ydrogen-bonded solid in real space.T he hydrogenbond-assisted formation of supramolecular networks on surfaces has been thoroughly investigated by scanning probe microscopic techniques in recent years.…”

Imaging the Solvation of a One‐Dimensional Solid on the Molecular Scale

“…As this is a dynamic process taking place on ultrashort timescales, the microscopic picture relies thus far mainly on theory . Atomic force microscopy experiments conducted in solution imaged the dissolution of solids on the nanometer scale . However, as these experiments are conducted mostly under ambient conditions, the interactions of individual solvent molecules with the solid are not traceable owing to intrinsic thermal fluctuations.…”