A photoemission and XAS study of oxygen coadsorbed with a (2 × 2) layer of K on graphite

We have studied the coadsorption of oxygen with a (2 × 2) monolayer of K on graphite. At least three different adsorption phases for oxygen have been found. Different spectroscopic techniques have been used in order to identify the different oxygen species adsorbed on the surface. For low oxygen coverage, the molecules dissociate and form a K 2O species. At higher oxygen doses, K 2O 2 and KO 2 are present on the surface up to saturation coverage. XAS yields an O 2 bond length of about 1.39 Å for the KO 2 in this phase. This species is found to form an ionic complex which is weakly bound to the graphite.