Charge state of steps on anatase TiO2(1 0 1) at 78 K by AFM/KPFM

Abstract

Surface steps strongly influence the surface chemistry of metal oxides, a detailed picture of step charge and structure may help to understand reactivity and predict the performance of the overall material in catalysis. In this study, we report the existence of another type of step, step BII, on the anatase TiO2(101) surface using atomic force microscopy/Kelvin probe force microscopy combined with density functional theory (DFT). By in situ measurements of current and contact potential difference (CPD) information, we found that step B II exhibits the highest charge state, followed by step C and D, which have the same structure, and step A with the weakest charge state. This finding challenges the conventional understanding that step C possesses the highest charge state. By incorporating DFT calculations, we confirmed that step B II possesses a higher charge state. This discovery also supports the observation of higher charge states in step C than in step B I. In addition, our results indicate that the valence band is predominantly governed by oxygen atoms, while titanium atoms dominate the conduction band. At the step edge, oxygen atoms act as electron donors, with electrons mainly clustering near the titanium atoms and Ti-O bonds. The present study provides a complete characterization of the charge state of the step edges on the anatase TiO2(101) surface and plays an important role in investigating the molecular adsorption as well as charge transfer in catalytic reactions on metal oxides surface.