CHANGES TO THE OCCUPIED AND UNOCCUPIED ELECTRONIC-STRUCTURE OF TIO2(100) UPON ALKALI-METAL REDUCTION

Direct and inverse ultraviolet photoemission spectroscopy (UPS and LPS ) are used to measure the occupied and unoccupied electronic structure of TiO2(100)1x1 and TiO2(100)c(2x2)K. UPS results from stoichiometric TiO2(100)1x1 are in good agreement with earlier studies. IPS data rec orded from TiO2(100)1x1 show two distinct features with energy positio ns 1.7 eV and 5.3 eV above the Fermi level (E(F)). These features are associated with the Ti 3d derived t(2g) and e(g) levels. Upon formatio n of TiO2(100)c(2x2)K, achieved by annealing K treated TiO2(100)1x1, s everal changes are observed to occur to the surface electronic structu re. Population of a band gap state pins E(F) and removes band bending at the surface. The valence band of TiO2(100)c(2x2)K is noted to be su bstantially narrower (of the order of 0.5 eV) than that of TiO2(100)1x 1. In addition to this, a sharp feature lying to the high binding ener gy side of the valence band is populated. Concurrently, intensity in t he Ti t(2g) derived conduction band level is lost. This redistribution of spectral intensity observed between TiO2(100)1x1 and TiO2(100)c(2x 2)K is interpreted in terms of a K induced redistribution of charge at the surface. We use resonant photoemission to test the idea that this charge redistribution involves mainly the Ti d levels.