Imaging oxygen molecular adsorption and dissociation on the Ti site of rutile TiO2(110) surface with real configuration at 78 K by atomic force microscopy

Abstract

Understanding oxygen adsorption and dissociation on the five-fold coordinated titanium (Ti_5c) site of the rutile TiO₂ surface is important in clarifying chemical reaction processes. Accordingly, three different configurations of molecularly adsorbed O₂, including parallel side-on, inclined side-on and end-on configurations, and their dissociation were directly observed with atomic resolution at 78 K by atomic force microscopy. Our results experimentally demonstrated that the three adsorbed O₂ configurations could be changed by electric field stimulation. The initial configurations of the adsorbed O₂ and transition of O₂ configurations were related to their coverage. On the other hand, the tunneling current stimulation could dissociate these O₂ species, indicating that they are precursors for the O adatom (O_ad). It is proposed that the effect of electric field stimulation contributes to the transition of these three adsorbed O₂ configurations, and the effect of the tunneling current is the main factor for the dissociation of the adsorbed O₂. In addition, based on the atomic contrast and height histograms of O_ad, different charge states of O_ad were observed, which could coexist on the surface region. The present study demonstrates an intuitional observation of O₂ adsorption and dissociation on the Ti_5c site, and thus is expected to be useful to understand the surface reactions on the oxide surface.