Coverage-dependent study of the Cs/Si(100)2x1 surface using photoelectron spectroscopy

Different coverages of Cs on the Si(100)2 X 1 surface were studied by high-resolution core-level spectroscopy and angle-resolved valence-band spectroscopy. The observation of two Ca 4d components, separated by similar to 0.4 eV, with approximately the same intensity at saturation coverage is consistent with the double-layer model for alkali-metal adsorption proposed earlier in the literature. Si 2p spectra from the saturated surface exhibit two surface shifted components that are interpreted as the up and down atom components of asymmetric Si dimers. The existence of asymmetric Si dimers on the Si(100)2 X 1-Cs surface is in contrast to the symmetric Si dimer structure reported earlier for the Si(100)2 x 1-K surface. The Cs saturated surface exhibits a metallic character as evidenced by a finite emission at the Fermi level in the valence-band spectra and by the large singularity index (Doniach-Sunjic line shape) needed in order to fit the Si 2p and Ca 4d core-level spectra.