The effect of stress fields from a probe tip on step motion using kinetic Monte Carlo

Abstract Studies of crystal surfaces at near equilibrium conditions using atomic force microscopy have demonstrated that the probe tip interacts with the shape and the motion of step edges. A step edge is found to retract near the probe tip, and the motion of the step is retarded in the vicinity of the tip. This effect, which is limited to a within a few atom diameters of the probe tip, has been attributed to stresses in the crystal caused by the proximity of the probe tip. We have conducted a study of this phenomenon using kinetic Monte Carlo simulations of a lattice gas model. The stress field from the probe tip was introduced as a cylindrically symmetric Gaussian energy field, which was incorporated into bond strength. Steps on the surface were generated by offsetting the periodic boundary conditions. The local morphology of the step was found to depend on the strength and size of the stress field, as well as on the kink site density of the step. The magnitude of the energy field which was sufficient to significantly alter the shape of the step was only a few percent of the bond energy. These results suggest a novel explanation of the enhanced material removal which is the basis of chemical mechanical polishing.