COARSENING MECHANISMS IN SURFACE MORPHOLOGICAL EVOLUTION

摘要

Based on a temperature-dependent, quantitative scanning tunneling microscopy analysis for the homoepitaxial growth and erosion of Pt(111), several possible atomic-scale mechanisms for the coarsening of mounds and pits are discussed: (ⅰ) noise-assisted coarsening, (ⅱ) coalescence coarsening, (ⅲ) step-edge diffusion present only during deposition or erosion, (ⅳ) step-edge diffusion present even in the absence of growth or erosion, and (ⅴ) step-atom attachment. For Pt(111), mechanism (ⅳ) is found to be decisive for coarsening. It is argued that for many low-index surfaces this coarsening mechanism is likely to be operative. Instead of a surface diffusion current driven by changes in surface curvature frequently assumed in phenomenological theories of coarsening, it appears that, even at high temperatures, coarsening is driven only by differences in curvature along contours of constant height.