Effect of Adsorbed Donor and Acceptor Molecules on Electron Stimulated Desorption: O2/TiO2(110)

The role of band bending on the efficiency of charge transfer across' the TiO2(110) single crystal surface has been measured in ultrahigh vacuum, in the absence of a wide range of surface site inhomogeneities, surface impurities and solvent effects, and particle size effects. The adsorption of the Cl-2 (electron acceptor) molecule. and the O-2 (electron acceptor) molecule have been found to enhance hole transport from TiO2 to O-18(2) molecules adsorbed on oxygen vacancy sites, increasing the rate of electron stimulated desorption (ESD) of O-18(2). This confirms that O-2-ESD is hole mediated. Conversely, adsorption of CH3OH, a donor molecule, reduces the transfer rate for holes to the adsorbed O-2, reducing its rate of ESD to near zero. The maximum effect of donor and acceptor molecules occurs near 1 monolayer coverage.