The interaction of molecular oxygen with water on titania surfaces is of importance due to its role in photocatalysis. As bridging oxygen vacancies (O-vac) and H-atoms are the dominant defects on TiO2(110) surfaces, following defect-specific reactions is greatly simplified by removing one of these defect types. For instance, scanning tunneling microscopy (STM) images of an H-free surface, reveal that O2 dissociates at the O-vacs, with one O-atom filling the vacancy and the other sitting on an adjacent 5-fold coordinated Ti site [1].
Here, we selectively remove O-vacs from TiO2(110) by exposing the surface to water vapour so that most of the O-vacs are filled with OH groups, thereby creating additional H-atoms. An STM scan at 3 V then creates a locally de-hydroxylated area which enables us to examine the mobility of the reaction product. After exposure to O2, bright spots of different corrugation can be seen on the bright rows at the expense of the H-atoms. This suggests that the bright spots arise from a reaction between the O2 and the H-adatoms. Furthermore, because the bright spots have a similar density within and outside the de-hydroxylated area, the reaction products must be highly mobile.
[1] O. Bikondoa, C. L. Pang, R. Ithnin, C. A. Muryn, H. Onishi, and G. Thornton,
Nat. Mat. 5 (2006) 189
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