XPS and XAS study of oxygen coadsorbed with a dispersed phase of K on graphite

The adsorption of O-2 onto a dispersed (low coverage) phase of K on graphit e has been characterized by X-ray photoemission and X-ray absorption spectr oscopy. We identify two oxygen adsorption phases before physisorbed oxygen appears. The first species dominates at low O-2 exposures whereas the secon d one, which is probably due to oxygen adsorbed in a superoxo-like configur ation (O-2(-delta), delta less than or equal to1), is dominant at higher ox ygen coverage. As a function of increasing oxygen dose, we confirm that the charge, initially donated by the potassium adlayer to the graphite, is gra dually withdrawn from the substrate. (C) 2001 Elsevier Science B.V. All rig hts reserved.