INVESTIGATION OF THE RB/GE(111) AND NA/GE(111) INTERFACES BY PHOTOEMISSION SPECTROSCOPY USING SYNCHROTRON RADIATION

The electronic properties of Rb/Ge(111) and Na/Ge(111) interfaces are investigated by soft X-ray photoemission spectroscopy using synchrotron radiation. On both systems, alkali metal deposition results in the formation of a new well defined interface state below the Fermi level. This interface state is highly sensitive to oxygen exposure. For the Na/Ge(111) system, this interface state is found to resonate around a photon energy of 82eV. This resonance occurs within the adsorbate/substrate complex involving hybridization of their valence electrons. These results indicate that the nature of alkali metal-germanium bond should be understood in terms of covalent bonding, as observed for alkali metal-silicon surfaces. The existence of this interface resonant state brings the first example of an extra-atomic resonance involving both substrate and adsorbate electronic levels. © 1990 IOP Publishing Ltd.