ON THE ELECTRONIC-STRUCTURE OF CU ULTRA-THIN FILM ON ALPHA-AL2O3(0001) SURFACES

Electron energy-loss spectroscopy (EELS) and uv photoelectron spectroscopy (UPS) were used to study the electronic structure of a Cu thin film on sapphire, Al2O3(0001) and on Al2O3Al(111). The surfaces were characterized by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The results indicate that a Cu(i)I state is formed on the Al2O3Al(111) and on the α-Al2O3(0001) surface when the Cu film is less than 2 Å thick. Upon further growth Cu(O) (metallic copper) is formed as nuclei. For Cu on α-Al2O3(0001), the EELS peak at 5.5 eV for coverages corresponding to less than 2 Å of Cu layer thickness is probably derived from an electronic transition from antibonding molecular orbitals of energies consisting of Cu(3d) and O (2p) near the top of the Al2O3 valence band to energy levels below conduction band minimum. © 1990.