Charge Trapping at the Step Edges of TiO2 Anatase (101)

A combination of photoemission, atomic force, and scanning tunneling microscopy/spectroscopy measurements shows that excess electrons in the TiO ₂ anatase (101) surface are trapped at step edges. Consequently, steps act as preferred adsorption sites for O ₂. In density functional theory calculations electrons localize at clean step edges, this tendency is enhanced by O vacancies and hydroxylation. The results show the importance of defects for the wide-ranging applications of titania. In step: Step edges on the TiO ₂ anatase (101) surface act as exclusive charge trapping centers. While the electron trapping is not favorable at (101) terraces, it is possible at the steps. It results in a higher reactivity of the steps towards some adsorbates, as illustrated for the example of O ₂ adsorption.