Spectroscopic investigations of the co-adsorption of potassium and oxygen on Ni(1 1 1) at room temperature

The electronic and vibrational properties of oxygen and potassium co-adsorbed on the Ni(1 1 1) surface at room temperature were studied by high resolution electron energy loss and X-ray photoelectron spectroscopies. The sample surface was prepared by means of two different procedures, namely by adsorbing oxygen on a pre-dosed potassium ad-layer and by reversing this sequential order. In both experiments we observed that a K coverage as high as 0.25 ML ( i.e. p(2 × 2) phase) is the condition necessary for measuring a weak K–O bond, while a K coverage greater than 0.30 ML (almost full layer), gives rise to a strong K–O bond which is evidenced by the loss feature at 27 meV. The loss spectrum of the K–O-c(4 × 2) phase shows that both species interact mainly with the substrate.