Synthesis and characterization of titania films on Mo(1 1 0)

Ultra-thin titania films were grown on a Mo(1 1 0) substrate by vapor depositing Ti in an O2 ambient (5×10−7 Torr) at 600 K, followed by annealing to 900–1200 K. X-ray photoelectron spectroscopy showed that titanium oxide films annealed to 900 K were partially reduced, exhibiting Ti4+, Ti3+ and Ti2+ species, whereas films annealed to 1200 K were fully oxidized and exhibited only Ti4+. Corresponding scanning tunneling microscopy measurements revealed layer-by-layer growth of titania films on Mo(1 1 0) at 900 K. Flat terraces with three different orientations were observed. The line spacings between the neighboring atomic rows for all terraces were ∼6.5 Å, suggesting epitaxial growth of TiO2(1 1 0)-(1×1). A further anneal of the films to 1200 K led to three-dimensional, rough surfaces for the fully oxidized films, indicating the formation of stable crystallites at high temperature.