The selective adsorption and kinetic behaviour of molecules on TiO2(110) observed by STM and NC-AFM

Abstract

In the present paper we report a kinetic aspect of molecules on terraces and steps of a TiO₂(110)-(1×1) surface as observed by scanning probe microscopy, which may be relevant to oxide catalysis. When the TiO₂ surface, heated at 400–450 K, was exposed to a formic acid ambient of 1–2×10^-6 Pa, small particles were formed on terraces. Post-reaction STM observation revealed that the particle formation was strongly suppressed in the vicinity of single-atom height steps. The suppressive effect of the steps ranged 2.4 nm into the terrace. Formate ions (a possible reaction intermediate) were imaged in-situ during formic acid exposure at the reaction temperature. The local density of the formates and hence the product distribution, which were very low near the steps, were simulated by a model. The particles produced were suggested to be carbonates, CO₃^2- on the bridging oxygen atoms of the TiO₂(110) surface.