ULTRATHIN REACTIVE METAL-FILMS ON TIO2(110) - GROWTH, INTERFACIAL INTERACTION AND ELECTRONIC-STRUCTURE OF CHROMIUM FILMS

A study of ultrathin Cr films on TiO2(110) surfaces is reported. The c ombination of low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) enables us to study quantitatively the growth of r eactive metal films on metal oxides, and the chemical interactions at the interface. Ultrathin Cr films grow initially in a quasi-two-dimens ional fashion at room temperature. Changes in oxidation states of both Ti and Cr during film formation suggest that strong chemical interact ions at the interface are of great importance in the growth of reactiv e metal films. Cr ''wets'' the surface more effectively at 300 K than ultrathin films of less reactive metals, Fe and Cu. This suggests that a relation exists between the metal reactivity with oxygen and the we tting of metal films on oxides: The more reactive the metal towards ox ygen, the better is the wetting ability. The chemical interaction is a ccompanied by charge transfer at the interface, causing a reduction of the surface work function. The interfacial interaction also causes th e interfacial Cr layer to behave differently from the top metallic Cr atoms upon thermal annealing. The top layers of metallic Cr show a str ong clustering tendency at 500-degrees-C, while the interfacial Cr see ms to have less surface mobility and slow bulk diffusion.