AVS 53rd International Symposium
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM8
STM Characterization of TiO@sub 2@(011)-2x1 Surface Morphology

Friday, November 17, 2006, 10:20 am, Room 2002

Session: Oxide Surfaces and Interfaces
Presenter: O. Dulub, Tulane University
Authors: O. Dulub, Tulane University
M. Batzill, Tulane University
U. Diebold, Tulane University
A. Selloni, Princeton University
C. Di Valentin, Università degli Studi di Milano-Bicocca, Italy
Correspondent: Click to Email
Titanium dioxide has a wide range of applications where its surface properties play an important role. Therefore, their study on the atomic scale is essential. The TiO@sub 2@(011) surface prepared by sputtering and annealing exhibits a stable (2x1) reconstruction in agreement with a previously proposed model by Beck et al. [Phys. Rev. Lett. 93 (3) (2004) 036104]. Atomically resolved STM images of the surface reveal flat terraces separated by monatomic steps. Unlike other TiO@sub 2@ surfaces, the (011) surface contains one-fold coordinated Ti=O (titanyl) groups, which are expected to have a diverse effect on surface chemistry. The Ti=O species form zig-zag chains along the [01bar1] direction, with O atoms imaged bright in empty-state STM. The most frequently occurring defects observed on the surface after argon ion sputtering and high-temperature UHV annealing are point defects (oxygen vacancies) and monolayer deep holes with several atoms missing. Oxygen vacancies appear as dark spots in STM images, in good agreement with DFT calculations. The density of such defects on the surface is reduced substantially upon re-annealing in molecular oxygen. Oxygen vacancies, as well as anti-phase domain boundaries in the (2x1) structure, are reactive sites for adsorption of gas molecules. Hydrogen atoms of hydroxyls groups, formed from dissociation of either H@sub 2@ or H@sub 2@O in the residual gas, are imaged as bright spots in STM. Argon ion bombardment and subsequent annealing in oxygen results in a rough surface with some (3x1) reconstructed areas. Segregation of calcium impurities from the bulk leads to a well-ordered overlayer structure with a centered (2x1) unit cell.