Atomic structure of theEu∕Si(111)3×2,5×1, and7×1surfaces studied by photoelectron spectroscopy

Abstract

Eu-induced Si(111)3x2, 5x1, and 7x1 reconstructions have been investigated by low-energy electron diffraction (LEED) and high-resolution photoelectron spectroscopy using synchrotron radiation. According to LEED, the 3x2, 5x1, and 7x1 phases can be produced on the dominating area of the Si substrate at the 0.20, 0.40, and 0.45 monolayer (ML), respectively, and no contributions from other phases are found in the LEED patterns at these coverages. The Eu 4f spectra show that the 3x2, 5x1, and 7x1 surfaces are semiconducting, and that the Eu atoms are completely divalent in these reconstructions. Si 2p core-level spectroscopy measurements performed at various photon energies and emission angles reveal three surface-related components with core-level shifts of -0.51, -0.20, and +0.17 eV with respect to the bulk component for the 3x2 surface. In addition to these components, two other components with shifts of -0.78 eV and +0.28 eV are found for the 5x1 and 7x1 surfaces. These results are discussed in the context of previous studies and structural models reported in the literature. It is shown that the present photoemission data obtained for the 3x2 surface are well consistent with the honeycomb-chain-channel (HCC) model with an adsorbate coverage of 1/6 ML. For the 5x1 and 7x1more » surfaces, we propose atomic models which include combinations of honeycomb and {pi}-bonded Seiwatz chains, with adsorbate coverages of 2/5 and 3/7 ML, respectively. Based on the LEED and Si 2p core-level results, a local x2 periodicity is expected for the 5x1 and 7x1 reconstructions, which is in good agreement with the nonmetallic electronic structure of these phases.« less