Study of the growth of NiO on highly oriented pyrolytic graphite by X-ray absorption spectroscopy

In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on highly oriented pyrolytic graphite (HOPG). NiO as been grown by reactive evaporation of metallic Ni in an oxygen atmosphere (2× 10−5 Torr) at room temperature. We paid special attention to he study of the early stages of growth. Both, Ni 2p and O 1s core-level XAS spectra were measured. For large NiO coverages, the spectra resemble hat of a NiO single crystal, thus indicating the formation of a stoichiometric NiO thin film on the HOPG substrate. The Ni 2p XAS spectra remain imilar during the whole growth process, indicating that Ni atoms are present in the high spin Ni2+ form, as supported by multiplet calculations. n contrast, for low coverages the line-shape of the O 1s XAS spectra differ strongly from that of bulk NiO. Cluster calculations of the spectra n octahedral and pyramidal symmetries support the formation of nanometric planar NiO islands at the graphite steps as previously observed by tomic force microscopy (AFM) in this system. 2006 Elsevier B.V. All rights reserved.