Alkali-metal-induced interface resonant state on a semiconductor surface

The formation of the Na/Ge(111)2×{}1 interface is investigated by photoemission spectroscopy using synchrotron radiation. Na is found to induce an electronic interface state below the Fermi level which is highly sensitive to oxygen exposure and resonates at a photon energy of 82 eV. This resonance occurs within the Na/Ge complex and results from the hybridization between sodium and germanium valence electrons leading to a covalent bonding. This investigation brings the first example of an extra-atomic resonance involving both adsorbate and substrate electronic levels.