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

The structure of the alpha-Al2O3 (1-102) surface was examined using crystal truncation rod (CTR) diffraction. The initial surface was prepared by Ar-ion sputter and anneal cycles in O-2, which resulted in a clean (1 x 1) surface. CTR data were then collected for the clean and water-dosed surfaces (1 x 10(-8)-1.6 Torr) in a UHV diffraction chamber (base pressure approximate to1-3 x 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. (C) 2001 Elsevier Science B.V. All rights reserved.