Electron energy-loss near-edge structure studies of a Cu/(112̄0)α-Al2O3 interface

Abstract

Electron energy-loss near-edge structure (ELNES) studies were employed to determine the bonding mechanisms and electronic structure of a Cu/(112̄0)α-Al2O3 interface prepared by molecular beam epitaxy. The existence of an interfacial ELNES component at the Al-L2,3 edge reveals that the Al atoms participate in the bonding and change their local coordination compared to bulk Al2O3. At the interfacial O-K ELNES some pre-edge intensity appears, indicating the presence of deep-level O-2p states hybridised with Cu-3d and/or Al-3p states. The interfacial Cu-L2, 3 ELNES shows a chemical shift of the edge onset to higher energy-loss values and the existence of unoccupied Cu-3d states. The shape and edge onset are similar to the Cu-L2,3 edge measured in an intermetallic CuAl2 compound. Image simulations of the experimental high-resolution transmission electron microscopic images were carried out assuming Cu-Al bonds at the Cu/(112̄0)Al2O3 interface as found by the ELNES studies. The derived structural model for the atomistic arrangement at the interface contains a mixed monolayer of Cu and Al atoms that exhibits a projected bonding distance of (0.15 ± 0.02) nm to the first O-layer of the Al2O3 substrate.