Growth process of the ridge--trough faces of a twinned crystal.

For a twinned face-centered-cubic crystal, the energy barrier for two-dimensional nucleation on a concave trough (or a re-entrant edge) and that for a layer advancing across a convex ridge were calculated. The former was obtained by analyzing the line tension of the trough. The results show that their energy barriers are 39 and 50% compared to that for nucleation on a flat {111} face, respectively. Therefore, the layer advance across the ridge is found to be more difficult than the nucleation on the trough. Based on these results, the morphology of the growing surface is predicted and an alternative growth process by the twin-plane-re-entrant-edge mechanism is suggested.