Alkali-metal–to–substrate charge transfer inTiO2(100)c(2×2)K

Resonance photoemission and surface-extended x-ray-absorption fine structure (SEXAFS) have been used to investigate the electron-donor properties of potassium adsorbed on rutile ${\mathrm{TiO}}_2$(100). Potassium K-edge SEXAFS from ${\mathrm{TiO}}_2$(100)c(2×2)K shows that K lies in a bridge site, bonding to two oxygen atoms with a K-O bond distance of 2.62±0.03 Å. Resonance photoemission data indicate that K adsorption is accompanied by charge transfer into Ti 3d band-gap states which are polaronic in nature. At 0.25 and 0.75 monolayer coverage about 1/4 of an electron is tranferred into Ti 3d states for each adsorbed potassium atom.