The adsorption of 3,4,9,10-perylene tetracarboxylic di-imide derivative molecules on the rutile TiO2(110) surface was investigated by non-contact atomic force microscopy and density-functional theory calculations. After sub-monolayer deposition, individual molecules were observed to adsorb with their main axis aligned along the [001] direction and centered on top of the bridging oxygen rows. Depending upon the tip termination, two distinctly different molecular contrasts were achieved. In the first mode, the molecules were imaged as bright elongated features, while in another mode the molecules appeared with a bright rim and a dark bow-shaped center. Comparison with the defect density on the bare TiO2(110) surface suggested that the molecules preferentially anchor to surface defects. The present density-functional theory calculations revealed details of the molecular adsorption position, confirming the experimentally observed adsorption on top of the bridging oxygen rows. The density-functional theory results indicated that diffusion along the rows should be quite easily possible, while diffusion perpendicular to the rows seems to be hindered by a significant energy barrier.

Imaging Perylene Derivatives on Rutile TiO2(110) by Non-Contact Atomic Force Microscopy. Schütte, J., Bechstein, R., Rahe, P., Rohlfing, M., Kühnle, A., Langhals, H.: Physical Review B, 2009, 79[4], 045428