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

Understanding oxygen adsorption and dissociation on the five-fold coordinated titanium (Ti-5c) site of the rutile TiO(2)surface is important in clarifying chemical reaction processes. Accordingly, three different configurations of molecularly adsorbed O-2, 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 O(2)configurations could be changed by electric field stimulation. The initial configurations of the adsorbed O(2)and transition of O(2)configurations were related to their coverage. On the other hand, the tunneling current stimulation could dissociate these O(2)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 O(2)configurations, and the effect of the tunneling current is the main factor for the dissociation of the adsorbed O-2. 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 O(2)adsorption and dissociation on the Ti(5c)site, and thus is expected to be useful to understand the surface reactions on the oxide surface.