Morphological Equilibration of Rippled and Dimpled Crystal Surfaces: The Role of Terrace-Width Fluctuations

The surface diffusion-mediated decay of unidirectional and bidirectional sinusoidal modulations of a solid surface below its roughening temperature was studied by kinetic Monte Carlo simulation. The characteristic decay time for bidirectional modulations with wavelength l was found to scale as l , in agreement with a prediction of Rettori and Villain and in contrast to the classical relaxation theory of Mullins for surfaces above the roughening temperature. The characteristic decay time for unidirectional modulations was found to have approximately the classical l dependence, but a different temperature dependence. The results are explained in terms of terrace-width fluctuations and a “terrace pinch-off” mechanism that short circuits step-step entropic repulsion as the driving force for surface relaxation. A simple model is developed that accounts for the temperature and wavelength dependencies of the simulation results, with no adjustable parameters. Implications for the interpretation of experimental data are discussed.