POTASSIUM ADSORPTION ON TIO2(100)

Potassium adsorption on TiO2(100) has been studied with low energy electron diffraction, Auger electron spectroscopy and photoemission. Potassium progressively lowers the work-function of TiO2(100) with increasing coverage to a limit of 2.2 +/- 0.1 eV. A clear work-function minimum is not observed, as found for other semiconductor surfaces. The work-function decrease is accompanied by a downward band-bending, limiting at 0.75 +/- 0.05 eV. This arises from the population of band-gap states following charge transfer from K to the substrate. At half-monolayer coverage an ordered c(2 x 2) overlayer is formed.