Oxygen adsorption on Cs covered GaAs(110) surfaces

Cs covered GaAs(110) was exposed to oxygen and studied with soft X-ray photoemission (SXPS). Oxygen was found to bond to the surface As atoms with 106 times greater initial oxygen uptake. A second Cs layer added after the Cs/GaAs (110) surface had been exposed to oxygen brings effects similar to the oxidation of GaAs by excited oxygen. Possible inadequacies of the conventional models of NEA photocathodes assuming noninteracting substrate and Cs2O layer are discussed.