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

Abstract

Laboratoire pour I'Utilisation du Rayonnement Electromagnetique, 91045New results on the (@ X @ ) R -+ 9" reconstructed a-Al,O, (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 lowenergy 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 Cefect of hexagonal periodicity with a parameter of 26.44 A. 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 0 Kedge, 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 (@ X @)Rf:9" reconstructed surface is more covalent than the (1 X 1) surface. Significant changes in the AI-0 hybridizations are observed; these are likely due to a difference in the interatomic distances along the [OOOlI axis (relaxations). The increase of covalent character is mainly due to a strong decrease of the Madelung field on the reconstructed surface.

Wetting and strength issues at Al/α–alumina interfaces

“…The (001) plane has been shown to become Al rich in UHV. [31][32] Evidently, the situation is analogous for the Al/Al 2 O 3 interface. The average surface and grain boundary energies are somewhat reduced with respect to those recorded for other metals at higher p(O 2 ).…”

Atomic Transport at Liquid Metal / Al₂O₃ Interfaces

“…These results indicate a change in the Wulff plot for the sapphire-vapor surface versus those recently reported [17,18] for higher oxygen activities and would be consistent with the idea that the surfaces oriented parallel to alternating sheets of O and Al atoms in the crystal structure may be partially reduced more readily. The (0001) plane has been shown to become Al rich in UHV [19,20]. Evidently, the situation is analogous for the liquid Al/Al 2 O 3 interface.…”

Electron induced surface chemistry at the Cs/sapphire interface

“…Photon irradiation of sapphire at energies as low as 1.2 eV has been shown to produce Al' and AlO-desorption Hamza 1992 and1993). In addition, thermal energy input can change the surface properties of sapphire (Gautier et al 1994). The presence of Cs is expected to alter the surface electronic properties of sapphire which, in turn, may enhance the chemical activity of the surface.…”