AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM3
Growth and Properties of Vanadia on Anatase TiO@sub 2@ (001) and (101) Surfaces

Monday, October 31, 2005, 9:00 am, Room 203

Session: Oxide Surface Structure and Characterization
Presenter: W. Gao, Yale University
Authors: W. Gao, Yale University
R. Klie, Brookhaven National Laboratory
E.I. Altman, Yale University
Correspondent: Click to Email
Inspired by its unique catalytic properties and elusive structure, we have been studying the structure of vanadia layers deposited onto epitaxial anatase (001) and (101) films. For anatase (001), a (1x4)/(4x1) reconstruction was observed by reflection high-energy electron diffraction (RHEED) and low energy electron diffraction (LEED). After depositing 1 ML at 525 K, X-ray photoelectron spectroscopy (XPS) showed predominantly V@super 5+@ and the (1x4)/(4x1) diffraction patterns were replaced by (1x1) patterns indicating that vanadia lifts the reconstruction and the monolayer is pseudomorphic. Continued growth caused the RHEED pattern to fade, suggesting that V@sub 2@O@sub 5@ epitaxy cannot be continued beyond 1 ML. At 750 K, however, VO@sub 2@ formed and the (1x1) pattern remained clear for 20 nm of vanadia. At 800 K, a c(2x2) termination was observed. These results suggest that the V@super 5+@ in the monolayer is due to 0.5 ML of terminal oxygen which allows epitaxy and the 5+ oxidation state. These results were compared with those for anatase (101) surfaces, the lowest energy anatase surface. The (101) surfaces were formed by depositing TiO@sub 2@ onto LaAlO@sub 3@(110). Although x-ray diffraction and scanning transmission electron microscopy indicated that the films grew with anatase (102) planes parallel to the interface, RHEED and LEED showed the surface diffraction patterns expected for a (101) surface and STM showed the oblique unit cell of the (101) surface. These conflicting results were attributed to the surface faceting to expose the lowest energy (101) surface. Similar to anatase (001), a (1x1) diffraction pattern is maintained after depositing 1 ML of V@sub 2@O@sub 5@; however, further vanadia deposition led to three dimensional vanadia clusters. STM is being used to further characterize the structure of the vanadia monolayers on the two anatase surfaces.