AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS3-TuM

Paper SS3-TuM9
Lower 3-fold Hollow Site of K on TiO@sub 2@(110)1x1

Tuesday, November 5, 2002, 11:00 am, Room C-112C

Session: Metals, Adsorbates, and Defects on TiO@sub 2@
Presenter: G. Thornton, Manchester University, UK
Authors: G. Thornton, Manchester University, UK
C.L. Pang, Manchester University, UK
C.A. Muryn, Manchester University, UK
V.R. Dhanak, Daresbury Laboratory, UK
Correspondent: Click to Email
Recent calculations by San Miguel et al (J. Phys. Chem. B 105 (2001) 1794) and Bredow et al (Surf. Sci. 418 (1998) 150) both predict that the low coverage bond site of K on TiO2(110) is the so called lower three fold hollow site. This involves two bridging O atoms and an in-plane O. In our work we have tested this prediction at a K coverage of 0.15 ML using a combination of surface extended X-ray absorption fine structure (SEXAFS), scanning tunneling microscopy (STM), and non-contact atomic force microscopy (NC-AFM). The polarisation dependence of the SEXAFS data rules out the atop, bridge and upper three fold hollow sites, and are consistent with the lower three fold hollow predicted by theory, with a K-O distance of 2.63 ű0.03 Å. In addition to elements of the clean surface STM image, images of the K dosed surface contain wide dark rows running along the [001] direction. These are about 3 nm in length and centered along the dark bridging oxygen rows such that the two adjacent 5-fold coordinated Ti rows are not imaged. These presumably arise from K-induced blocking of the tunneling current, either by charge transfer to Ti 3d states, or because there are no empty states of K near EF. The clustering of alkali metal sites is consistent with molecular dynamics simulations. In the absence of useful topographic information in STM, we turn to NC-AFM images of TiO2(110)1x1, where the [001] direction bright rows arise from bridging O atoms. In addition to straight rows characteristic of the clean surface, zigzag rows are observed on the K-dosed surface, presumably arising from K atoms alternately occupying sites on either side of a bridging O row, as predicted by theory.