Direct Observation of Surface-Mediated Electron-Hole Pair Recombination in TiO2(110)

The kinetics Of Surface and bulk electron-hole pair recombination have been Measured separately on TiO2(110) in ultrahigh vacuum under well-controlled Surface conditions for the first time. Using 100 eV incident electrons, excitation of electron-hole pairs Occurs within similar to 6 angstrom of the surface, and the rate of stimulated desorption of O-2 was measured as a means of determining the charge carrier recombination kinetics, which are found to be mediated by the surface and to be first-order in charge carrier concentration. Comparison with a previous O-2 photodesorption experiment, where excitation by 3.4 eV photons was used for electron-hole pair generation in a deeper region below the Surface (similar to 100 angstrom), shows that bulk recombination ill TiO2 occurs by second-order kinetics in charge carrier concentration.