TiO2(100) structure-reactivity relationship

The influence of point defects (oxygen vacancies) and steps on the reactivity of TiO2(100) has been studied with LEED and soft X-ray photo-emission using H2O as a model adsorbate. An O termination of the TiO2(100)1*1 surface is deduced by comparison of surface core-level shift data for this surface and TiO2(001); ordering of O vacancies produced in the surface layer by annealing gives rise to a TiO2(100)1*5 reconstruction. The interaction of H2O with 1*1 and 1*5 TiO2(100) surfaces in the range 120 to 450 K is almost identical, indicating that the ordered oxygen vacancies of the 1*5 surface do not play a major role in the surface chemistry. A comparison of planar and 3 degrees vicinal TiO2(100)1*1 reactivity shows that steps also play a spectator role. Although unreactive at room temperature, H2O adsorbs molecularly at 120 K. Thermally induced dissociation occurs on annealing, to form Ti-O-H species with a bond angle of approximately 90 degrees .