α‐Al2O3 (0001) Surfaces: Atomic and Electronic Structure

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Abstract
New results on the R± 9° reconstructed α‐Al2O3 (0001) surface, which can be obtained after heating at high temperature (1400°C) under vacuum, are presented. The atomic structure has been studied by combining low‐energy electron diffractometry and grazing incidence X‐ray scattering. The surface structure is found to be perfectly commensurable with the underlying bulk lattice. The surface consists of hexagonal zones of two, nearly perfect, close‐packed Al (111) planes separated by a defect of hexagonal periodicity with a parameter of 26.44 Å. This model is consistent with previous surface studies of this reconstruction. The electronic structure has been investigated using valence band photoemission spectroscopy, X‐ray absorption spectroscopy at the O K edge, electron energy loss spectroscopy, and X‐ray‐induced Auger electron spectroscopy. Interpretation of these experimental data in the frame of a self‐consistent, tight‐binding calculation leads to the conclusion that the R± 9° reconstructed surface is more covalent than the (1 × 1) surface. Significant changes in the; Al‐O hybridizations are observed; these are likely due to a difference in the interatomic distances along the [0001] axis (relaxations). The increase of covalent character is mainly due to a strong decrease of the Madelung field on the reconstructed surface.