Control of a surface photochemical process by fractal electron transport across the surface:: O2 photodesorption from TiO2(110)

The photodesorption of O-2 from TiO2(110) has been found to exhibit fractal kinetic behavior. The rate coefficient for photodesorption is measured throughout the entire experiment and is shown to decrease by a factor of similar to 100 over a time period of similar to 250 s. A model is proposed in which the electrons associated with O-vacancy defects on the surface percolate from vacancy site to vacancy site via the filled orbitals at these sites to neutralize photoproduced holes. This electron percolation, causing electron-hole recombination, reduces the efficiency of charge transfer between a photoproduced hole and an O-2(-)(a) species localized at a vacancy defect site, causing the rate of O-2 photodesorption to follow a fractal rate law. We postulate that the fractal electron conduction path across the surface is one-dimensional.