ULTRATHIN METAL-FILMS ON TIO2(110) - METAL OVERLAYER SPREADING AND SURFACE REACTIVITY

We have studied the growth of ultrathin (< 50 angstrom) Cu overlayers on stoichiometric TiO2(110) surfaces. Using low energy ion scattering, the growth mode of Cu was determined to be Volmer-Weber type (three-d imensional islands) at room temperature; evidence for cluster growth i s observed even at 160 K. A comparison with Fe and Cr metal films show s that the spreading of the films correlates with the heat of formatio n of the metal oxide of the overlayer. Fe and Cr cause a reduction of the Ti4+ surface cations at the metal/metal oxide interface as observe d with X-ray photoelectron spectroscopy. No reduction of the TiO2 cati ons takes place upon contact with a Cu overlayer.