Manipulating bonding at a Cu/(0001)Al2O3 interface by different substrate cleaning processes

Growth of Cu films on (0001)Al2O3 substrates can result in metallic Cu-Al or ionic-covalent Cu-O bonds at atomically abrupt interfaces. The type of bonding depends on the substrate cleaning procedure prior to film growth. Cu films deposited on Ar+-ion sputter-cleaned substrates exhibit interfacial Cu-L-2,L-3, Al-L-2,L-3 and O-K energy-loss near-edge structures that indicate the formation of metallic Cu-Al bonds at the Cu/Al2O3 interface. In contrast, growth on chemically cleaned alpha-Al2O3 substrates results in interfacial energy-loss near-edge structures that suggest Cu-O bonding at the interface. The experimental electron energy-loss spectroscopic results are compared to calculated spectra, and the mechanisms causing the changes in the atomic and electronic structure are addressed.