Effects of the crystal reduction state on the interaction of oxygen with rutile TiO2(1 1 0)

Abstract The interaction of O 2 with reduced rutile TiO 2 (1 1 0)–(1 × 1) has been studied by means of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD) and photoelectron spectroscopy (PES). It is found that the interaction of O 2 with TiO 2 (1 1 0) depends strongly on the reduction state of the TiO 2 (1 1 0) crystal. High-resolution STM studies revealed that the energy barrier for the non-vacancy-assisted, 2nd O 2 dissociation channel decreases with increasing crystal reduction. Additionally, it is found in the STM studies that the Ti interstitial diffusion is slightly more facile in high-reduced TiO 2 (1 1 0) crystals compared to low-reduced ones. Accompanying TPD studies revealed that the line shape of the O 2 -TPD peak occurring between ∼360 K and ∼450 K depends on the crystal reduction state. For high-reduced TiO 2 (1 1 0) crystals characterized by large terraces most O 2 molecules desorb at ∼386 K, whereas O 2 desorption is peaking at ∼410 K for low- and medium-reduced crystals. Furthermore, the O 2 -TPD experiments revealed a highly non-linear behavior of the O 2 desorption peak integrals as function of the crystal reduction state. The presented results point to an ionosorption model where the adsorbates withdraw the excess charge (Ti 3+ ) from the near-surface region at temperatures