Defect Sites on TiO₂(110). Detection by O₂ Photodesorption

The TiO 2 (110) surface, prepared with different densities of anion vacancy defect sites, has been investigated by studies of O 2 photodesorption at 105 K. Two separate O 2 photodesorption processes, α 1 and α 2, are detected and are postulated to be due to the presence of two different types of defect sites produced by annealing the crystal in vacuum before O 2 adsorption. The measured photodesorption cross sections for these two states are Q α 1 -O 2 = (3.1 ± 0.2) × 10 - 16 cm 2 and Q α 2 -O 2 = (4.3 ± 0.3) × 10 - 17 cm 2 for 3.96 ± 0.07 eV photons. Both O 2 states photooxidize CO chemisorbed on the reduced TiO 2 (110) surface. While the yield of the CO 2 photoproduct increases with increasing crystal annealing temperature (and increasing defect coverage), the yield of α 1 -O 2 and α 2 -O 2 passes through a maximum at an annealing temperature of ∼600 K.