Identification of the electronic structure differences between polar isostructural FeO and CoO films by core-level soft x-ray spectroscopy

The electronic properties of the FeO and CoO single layer thin films on Pt(111) were examined by core-level soft x-ray spectroscopy. These oxygen terminated films are bilayer-thick and isostructural Pt, Fe-Co, and O atoms stacked with small lateral shifts due an incommensurate relation with Pt(111). Probing occupied and unoccupied states projected on the oxygen atoms revealed states at the Fermi level, suggesting orbital mixing with the metal substrate, and also indicated an anisotropy in transition metal-oxygen bonding geometry. The differences in the core-level spectral features were attributed to the substrate induced modification of the charge transfer energy and with an additional valence electron on Co.