PNNL

Abstract

The solid-on-solid kinetic Monte Carlo model of Lasaga and Blum for dislocation- controlled etch pit growth has been extended to the growth of etch pits under the control of multiple dislocations and point defects. This has required the development of algorithms that are 0(103) – O(104) times faster than primitive kinetic Monte Carlo models for surfaces with areas in the range 1024x1024 – 4096x4096 lattice sites. Simulations with multiple line defects indicate that the surface morphology coarsens with increasing time and that the coarsening is more pronounced for large bond-breaking activation energies. For small bond breaking activation energies dissolution enhanced by line defects perpendicular the dissolving surface results in pits with steep sides terminated by deep narrow hollow tubes (nanopipes). Larger bond breaking activation energies lead to shallow pits without deep nanopipes, and if the bond breaking activation energy is large enough, step flow is the primary dissolution mechanism, and pit formation is suppressed. Simplified models that neglect the far field strain energy density but include either a rapidly dissolving core or an empty core lead to results that are qualitatively similar to those obtained using models that include the effects of the far field stress and strain. Simulations with a regular array of line defects show that microscopic random thermal fluctuations play an important role in the coarsening process.