Surface structure of () Al2O3 single crystals after high temperature annealing

The surface structure of a-plane ( 1 1 2 ¯ 0 ) Al2O3 single crystals with a < 1 0 1 ¯ 0 > inclined direction was studied as a function of annealing temperature using atomic force microscopy. The samples had a large increase in step height and terrace width with increasing annealing temperature. For the samples annealed at 1500 °C and 1600 °C the step edge structure became significantly faceted. The facets consisted of (0 0 0 1) and ( 10 1 ¯ 2 ) planes as a result of these two planes being the ones with the lowest surface energies in Al2O3. In addition, the surface morphology displayed the formation of ridges 0.3 nm high and ∼20 nm wide at 1600 °C which originate from a tendency of the surface to form a (4 × 1) reconstruction with the sharp step edges acting as reconstruction nucleation sites.