X-ray absorption study of the local structure at the NiO/oxide interfaces

This work reports an X-ray absorption near-edge structure (XANES) spectroscopy study at the Ni K-edge in the early stages of growth of NiO on non-ordered SiO₂, Al₂O₃ and MgO thin films substrates. Two different coverages of NiO on the substrates have been studied. The analysis of the XANES region shows that for high coverages (80 Eq-ML) the spectra are similar to that of bulk NiO, being identical for all substrates. In contrast, for low coverages (1 Eq-ML) the spectra differ from that of large coverages indicating that the local order around Ni is limited to the first two coordination shells. In addition, the results also suggest the formation of cross-linking bonds Ni-O-M (M = Si, Al, Mg) at the interface.