Rayleigh instabilities in crystalline solids: Evolution of finite-aspect-ratio pore channels in sapphire Original Research Article

The morphological evolution of lithographically introduced high-aspect-ratio pore channels in sapphire during anneals at 1700 °C was examined. The pore-channel aspect ratio and the crystallographic orientation of the channel axis within the mimage plane were systematically varied over wide limits. Of the 12 crystallographically distinct channel orientations sampled, all exhibited evolution characteristics inconsistent with expectations for a material with isotropic surface energy. Those oriented such that the channel could be either fully or partially bounded by low-index surfaces that are part of the Wulff shape of sapphire were most strongly stabilized against breakup into multiple pores. Relative to prior work, in which channels were introduced into the stable c(0 0 0 1) plane of sapphire, pore channels introduced into the unstable mimage plane were generally less resistant to breakup, and the transition from formation of a single void to the formation of two or more pores occurred at significantly smaller length-to-radius ratios.