Interfacial Electronic Structure of Thin Cu Films Grown on Ar+-ion Sputter-cleaned a-Al2O3 Substrates
Interfacial Electronic Structure of Thin Cu Films Grown on Ar^＋—ion Sputter—cleaned α—Al2O3 Substrates

The bonding and electronic structure of Cu/(0001)Al2O3 and Cu/(1120)Al2O3 interfaces has been studied experimentally using spatially-resolved transmission electron energy loss spectroscopy. The specimen were prepared by depositing Cu on single-crystal α-Al2O3 substrates, which have been Ar+-ion sputter-cleaned prior to the growth of Cu. For both orientations of the α-Al2O3 substrate, atomically abrupt interfaces formed as determined by highresolution transmission electron microscopy. The investigations of the interfacial Cu-L2,3, AI-L2,3 and O-K energy loss near-edge structures, which are proportional to the site- and angular-momentum-projected unoccupied density of states above the Fermi level, indicate the existence of metallic Cu-AI bonds at the Cu/AI2O3 interface independent of the substrate orientation.