Kinetic Monte Carlo investigation of pit formation at the CaCO 3(101̄4) surface-water interface

Abstract

On the basis of quantitative information derived from atomic-force microscopy (AFM) studies of shallow pit formation at the CaCO 3(101̄4) surface-water interface in the surface-reaction regime, we have developed a kinetic Monte Carlo (KMC) model which reproduces quantitatively the experimental behaviour of the time-evolution of the pits. This allows the rates of all the important elementary atomistic processes involved in the dissolution to be obtained, rates not readily obtainable directly from AFM data. The KMC model also provides important insight into the evolution of very small pits, which in principle can be resolved using AFM, but which in practice are very difficult to observe because of the low probability of their occurrence in the microscope scan area. The KMC simulations show that the growing pits exhibit two different growth regimes, in agreement with the predictions of a simple terrace-ledge-kink (TLK) model. For very small pits the linear pit size increases exponentially with time and the pit edges accelerate (double-kink self-annihilation regime). Having attained a certain pit size (∼25 nm for a temperature of 300 K), thereafter the pit sizes increase linearly with time, the pit edges maintaining a constant velocity (kink-kink annihilation regime). A comparison of the quantitative predictions of the TLK model with KMC simulations shows that, in spite of its simplicity, the TLK model provides a satisfactory semi-quantitative description of the pit evolution. The KMC model presented provides the starting point for the development of a more comprehensive model of the calcite-water interface which will include the effects of adsorbates and other variations in interface conditions. Published by Elsevier Science B.V.