Excited states at interfaces of a metal-supported ultrathin oxide film

Metal-supported ultrathin oxide films such as MgO/Ag(001) are a class of materials of technological importance in various research fields such as catalysis, spintronics, or nanoelectronics. At the ultrathin limit of three monolayers, due to the different environment, each layer develops different electronic characteristics. At the PEARL beamline, researchers have used Resonant Auger electron spectroscopy near the Mg K edge to identify the local density of empty Mg p states in each individual layer. While the middle layer shows the normal oxide band gap known from the bulk material, the gap is filled by metal-induced gap states at the metal/oxide interface. At the oxide/vacuum interface, the optical gap is reduced by a surface-core exciton involving an image potential state in the vacuum. Using the core-hole clock method, the lifetime of this surface-core exciton of 5 fs has been measured.