Atomic geometry and electronic structure of theSi(100)2×3-Eu surface phase

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The structural and electronic properties of the Eu-induced $2\ifmmode\times\else\texttimes\fi{}3$ reconstruction on Si(100) have been investigated by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and high-resolution Si $2p$ core-level spectroscopy using synchrotron radiation. STM images of this reconstruction are found to be drastically dependent on the bias voltage and tunneling current. STS measurements show that the $2\ifmmode\times\else\texttimes\fi{}3$-Eu surface is semiconducting. Two occupied states at $\ensuremath{-}0.9$ and $\ensuremath{-}1.75\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ and three unoccupied states at $+0.35$, $+0.8$, and $+1.5\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ are identified in the $(dI∕dV)∕(I∕V)$ spectrum of this surface. The Si $2p$ core-level spectra taken at various photon energies and emission angles are revealed to include four surface-related components $S1\ensuremath{-}S4$ with core-level shifts of $\ensuremath{-}0.54$, $\ensuremath{-}0.24$, $+0.21$, and $+0.51\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, respectively. The $S1$, $S2$, and $S4$ components are assigned to first-layer Si atoms in the $2\ifmmode\times\else\texttimes\fi{}3$-Eu structure and the $S3$ component is shown to arise from the second-layer Si atoms. The results are discussed in the context of structural models reported recently for other metal-induced $\mathrm{Si}(100)2\ifmmode\times\else\texttimes\fi{}3$ reconstructions. Finally, an atomic model is proposed for the $2\ifmmode\times\else\texttimes\fi{}3$-Eu phase.