ELECTRONIC-PROPERTIES OF THE A GE(111) INTERFACE/

When silver is deposited onto Ge(111)c(2 x 8), the interface may under go a (3 x 1), (4 x 4), (root 3 x root 3)R30 degrees and eventually a ( 6 x 6) reconstruction. By using a scanning tunneling microscope (STM) in the current-imaging tunneling spectroscopy (CITS) mode, we obtained important new information on the electronic properties of these coexi sting reconstructions. The c(2 x 8), (3 x 1) and (4 x 4) reconstructio ns are non-metallic with tunneling gaps of 0.45, 0.85 and 0.85 eV, res pectively, while the (root 3 x root 3)R30 degrees reconstruction is ma nifestly metallic, Electron energy-loss spectroscopy (EELS) data revea l Delta q(parallel to) = 0 excitation gaps which match the tunneling g aps from CITS. In addition. EELS indicates that increasing the Ag dens ity ill the metallic (root 3 x root 3)R30 degrees phase initiates a gr adual metal-non-metal transition. This transition is completed with th e formation of a high-density (6 x 6) reconstruction with a band gap o f 0.18 eV. We propose that the (4 x 4), (root 3 x root 3)R30 degrees a nd (6 x 6) structures have a Ge trimer unit in common. (C) 1997 Elsevi er Science B.V.