Growth and reactivity of titanium oxide ultrathin films on Ni(110)

Soft X-ray photoelectron spectroscopy (SXPS) and X-ray absorption near-edge structure (XANES) have been combined with low-energy electron diffraction (LEED) to examine the growth of titanium dioxide thin films on Ni(110). Depending on the initial titanium coverage, the formation of two different films is observed, a quasi-hexagonal phase and a film with rutile (110) rods. Spectroscopy (SXPS and XANES) results indicate that all films consist of fully oxidized titanium. Furthermore, the reactivity of the higher coverage phase, consisting partly of rutile TiO2(110), was investigated after exposure to molecular water at 190 K. The formation of molecular water and hydroxyls was observed for low-pressure exposure (less than 10(-7) mbar). High-pressure exposure (on the order of 10(-6) mbar) resulted in hydroxylation of the thin film, which was found to be reversible upon annealing.