Core and valence band photoemission study of highly strained ultrathin NiO films on Pd(100)

We discuss the results of an extensive investigation on NiO ultrathin films grown on Pd(100), carried out by means of high-resolution X-ray photoelectron spectroscopy (core levels) and ultraviolet photoelectron spectroscopy (valence band levels). The peculiarity of the investigated system is the rather high lattice mismatch between NiO and the Pd substrate (7.3%). Detailed information on the electronic structure of NiO ultrathin films is obtained as a function of thickness, with a particular emphasis put on the fully wetting single c(4 × 2)-Ni3O4 defective monolayer, up to the bulklike relaxed films, through the intermediate three-dimensional strained islands resulting from a Stranski−Krastanov growth behavior.