The adsorption of a submonolayer of catechol (C6H6O2) on the rutile TiO2(110)-1x1 surface has been investigated by Scanning Tunneling Microscopy (STM). The catechol molecules are preferentially adsorbed on the surface 5-fold coordinated Ti4+ sites, and occupy two neighboring lattice Ti sites. No preference for adsorption at surface step edges is observed at room temperature. A statistical analysis of intermolecular distances demonstrates that the interaction between the molecules strongly depends on the surface crystallographic direction: catechol molecules exhibit attractive interaction along [1-1 0], while they repel each other along the  direction. The attractive interaction is proposed to be caused by the coupling of pi bonding electrons and the repulsive interaction is possibly mediated by substrate.
Reprints available from U. Diebold (diebold).
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