XPS Lineshape Analysis of Potassium Coadsorbed with Water on Ni(111)

Kurzfassung

The line profiles of XP spectra of H2O/K/Ni(111) were investigated for K submonolayer coverages. The K2p spectra exhibit a strong alteration of lineshape with increasing water coverage. Without coadsorbed water a significant asymmetry was found which decreased rapidly and independently of the potassium precoverage with increasing water exposure up to ΘH2O = 0.7. The asymmetry observed in the K2p spectra is assigned to a coupling of the potassium adatoms to the electronic structure of the nickel substrate. The coadsorption of water suppresses this mechanism via a loosening of the potassium-nickel coupling. Since the decrease of asymmetry is independent of the potassium coverage, it is concluded that this process is due to an adsorbate-substrate interaction between the water and the nickel substrate only. This contradicts models in which the coadsorption of water and potassium on metal substrates is manifested in hydration of the potassium adatoms.