THEORETICAL-ANALYSIS OF STM EXPERIMENTS AT RUTILE TIO2 SURFACES

A first-principles atomic orbital-based electronic structure method is used to investigate the low index surfaces of rutile titanium dioxide (TiO2). The method is relatively cheap in computational terms, making it attractive for the study of oxide surfaces, many of which undergo large reconstructions, and may be governed by the presence of oxygen v acancy defects. Calculated surface charge densities are presented for low-index surfaces of TiO,, and the relation of these results to exper imental scanning tunnelling microscopy images is discussed. Atomic res olution images at these surfaces tend to be produced at positive bias, probing states which largely consist of unoccupied Ti 3d bands, with a small contribution from O 2p. These experiments are particularly int eresting since the O atoms tend to sit up to 1 Angstrom above the Ti a toms, so providing a play-off between electronic and geometric structu re in image formation.