Crystal truncation rod diffraction study of the α-Al2O3 (1 1̄ 0 2) surface

The structure of the α-Al2O3 (1 −1 0 2) surface was examined using crystal truncation rod (CTR) diffraction. The initial surface was prepared by Ar-ion sputter and anneal cycles in O2, which resulted in a clean (1×1) surface. CTR data were then collected for the clean and water-dosed surfaces (1×10−8–1.6 Torr) in a UHV diffraction chamber (base pressure≈1–3×10−9 Torr). Water dosing had little effect on the diffraction data, suggesting that the initially prepared surface was fully oxygenated. Least-squares analysis of the CTR data resulted in two best fit models, a relaxed stoichiometric bulk termination and a relaxed bulk termination with a zero occupancy for the first layer of aluminum atoms. Crystal chemistry considerations suggest that the second model is the most plausible if the surface oxygens are protonated.