Splitting of the Ni 3d states at the surface of NiO/HOPG nanostructures

This project deals with the study of the electronic structure of the NiO nanostructures formed at the early stages of growth of NiO on highly oriented pyrolytic graphite (HOPG). Our main aim is the study of nanostructured NiO systems where possible surface effects are enhanced by the large surface to volume ratio of the nanostructures. In fact, early studies [1] on 3 nm NiO nanoparticles with unique catalytic properties revealed a splitting of the unoccupied Ni eg states, as shown by the O 1s XAS spectra. This splitting was interpreted as the result of the lack of the apical oxygen at the NiO surface and the large surface to volume ratio of the nanoparticles. On the other hand, the early stages of growth of NiO/HOPG are known to produce planar NiO islands along the graphite steps as shown by Atomic Force Microscopy (AFM) images.[2] Such a particular arrangement of NiO nanostructures is expected to exhibit similar surface effects as in the NiO nanoparticles. Therefore, the study of this system seems to be well justified.