XPS study of the adsorption of NH3 on nickel oxide on Ni(111)

The aim of the present work was to investigate the initial stages of NH3 interaction with nickel oxide layers formed on well-defined Ni(111) surfaces. The selected technique was x-ray photoelectron spectroscopy. Ammonia adsorption was performed at 10−7 mbar and room temperature in a preparation chamber attached to the analysis chamber. After each adsorption, the N 1s core level was analysed and its intensity was plotted as a function of exposure (at the same pressure) to obtain the adsorption kinetnetics. The XPS peak shapes and the chemical shifts were related to the nature of the adsorption products. In our experimental conditions, we observed that the more reactive initial surface was the one covered by the O-adsorbed phase corresponding to the precursor state of the NiO formation. The NiO alone does not exhibit significant reactivity, whereas a mixture of NiO and the O-adsorbed phase shows a similar behaviour to that of the pure O-adsorbed phase. From the first adsorption until the last one, two nitrogen adspecies were detected: one with an N 1s binding energy (BE) of 397.8 eV and the other at 399.7 eV. The data indicate that the surface reactivity is structure-sensitive for the NiO layer and the mechanisms of adsorption seem to involve NH3 dissociation into NHx adspecies, along with OH formation. Copyright © 2000 John Wiley & Sons, Ltd.