Structure and growth of ultrathin titanium oxide films on Ru(0Â 0Â 0Â 1)

Structure, chemical composition and thermal stability of TiOx films with a thickness of up to 3 ML grown on a Ru(0 0 0 1) substrate were investigated by scanning tunneling microscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The films were prepared by evaporation of Ti in 10−7 mbar O2 onto Ru(0 0 0 1) at 640 K, followed by annealing in 10−7 mbar O2 or in UHV at temperatures between 700 K and 1000 K. Depending on the deposition and post-annealing conditions, we find several different structures of the Ti oxide, with the layers post-annealed in an O2 environment being generally better defined than those post-annealed in vacuum. The layers consist of triangular units which coalesce upon annealing. O2 annealing of monolayer films leads to an oxygen deficient TiO2 layer. Annealing to 900-1000 K changes the structure and composition of the film, a coincidence structure with a Moiré pattern is observed upon O2 annealing.