Growth of ultrathin Cu layers onCu2O/Cu(110) and CuO/Cu(110): Sandwich electronic and epitaxial structures

The growth of ultrathin layers of copper upon copper oxide structures, formed on top of an ordered chemisorbed layer upon a Cu(110) surface, was studied by ultraviolet photoelectron spectroscopy, electron-energy-loss spectroscopy (EELS), Auger-electron spectroscopy, and low-energy electron diffraction. The 5.9-eV loss obtained upon formation of ${\mathrm{Cu}}_2$O is attributed to a plasmon loss, contrary to the interpretations in earlier literature. The degree of charge transfer upon oxygen adsorption is estimated from EELS. The deposited submonolayer Cu induces a state located 0.3 eV above the valence-band-maximum level on the ${\mathrm{Cu}}_2$O substrate. A Cu-induced state within the band gap and a movement of the Fermi level suggests a strong interaction of Cu with the oxide substrate. The ${\mathrm{Cu}}_2$O is formed during the initial Cu submonolayer deposition on a CuO surface, and a two-dimensional interfacial reaction is demonstrated at the low Cu coverages during the growth, which suggests the following scheme: CuO+Cu→${\mathrm{Cu}}_2$O.