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-ban d 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 a dsorption proposed earlier in the literature. Si 2p spectra from the s aturated surface exhibit two surface shifted components that are inter preted 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 i n contrast to the symmetric Si dimer structure reported earlier for th e 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-Sunj ic line shape) needed in order to fit the Si 2p and Ca 4d core-level s pectra.