Oxidation states at alkali-metal-doped Ni(110)-O surfaces

The interaction of lithium, sodium and potassium with an oxidised Ni(110) single crystal surface has been investigated using X-ray photoelectron spectroscopy (XPS). Incorporation of the alkali metal into the oxide layer at room temperature results in the suppression of the intrinsic Ni(2p) satellite structure of stoichiometric NiO, confirming its origin in an inter-site screening process in accordance with a recent theoretical model. In addition, the reaction of the alkali metal with NiO at higher temperatures gives rise to a divalent or trivalent nickelate species. The effect of water vapour on nickelate formation and the reactivity of the nickelate to carbon monoxide is also investigated.