We report layer-resolved measurements of the unoccupied electronic structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states at the metal/oxide interface, the oxide band gap, and a surface core exciton involving an image-potential state of the vacuum are revealed through resonant Auger spectroscopy of the $\mathrm{Mg}K{L}_{23}{L}_{23}$ Auger transition. Our results demonstrate how to obtain new insights on empty states at interfaces of metal-supported ultrathin oxide films.

• Received 9 December 2014
• Revised 27 March 2015

DOI:https://doi.org/10.1103/PhysRevB.91.161410