Electron energy-loss near-edge structure studies of a Cu/(11(2)over-bar0)alpha-Al2O3 interface

Electron energy-loss near-edge structure (ELNES) studies were employed to d etermine the bonding mechanisms and electronic structure of a Cu/(11(2) ove r bar 0)alpha -Al2O3 interface prepared by molecular beam epitaxy. The exis tence of an interfacial ELNES component at the Al-L-2,L-3 edge reveals that the Al atoms participate in the bonding and change their local coordinatio n compared to bulk Al2O3. At the interfacial O-K ELNES some pre-edge intens ity appears, indicating the presence of deep-level O-2p states hybridised w ith Cu-3d and/or Al-3p states. The interfacial Cu-L-2,L-3 ELNES shows a che mical shift of the edge onset to higher energy-loss values and the existenc e of unoccupied Cu-3d states. The shape and edge onset are similar to the C u-L2,3 edge measured in an intermetallic CuAl2 compound. Image simulations of the experimental high-resolution transmission electron microscopic image s were carried out assuming Cu-Al bonds at the Cu/(11(2) over bar 0 )Al2O3 interface as found by the ELNES studies. The derived structural model for t he 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.