Dendritic Sublimation of Sapphire

We report on the morphological evolution of macrosteps on the vicinal (0001) surface of sapphire during sublimation in vacuum. Preparation of a wide flat terrace and isolation of a step source by chemical etching, followed by high‐temperature annealing, allowed the formation of various step patterns depending on the secondary annealing temperature. The observed step patterns such as smooth lines, faceted lines, isolated dendrites, dendritic array, and the morphological transitions between them bear striking resemblance to the interface patterns observed in the solidification of materials. The relative area of upper terrace to lower terrace plays an important role in determining the stability of step. By using a phase‐field simulation, we show that the dynamics of the observed pattern formation can be reproduced by the Burton–Cabrera–Frank model.