Angle-resolved ultraviolet photoelectron spectroscopic study of Si(001)-(2×1)/K and Si(001)-(2×1)/Cs surfaces

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Abstract
Angle-resolved ultraviolet-photoelectron-spectroscopy (ARUPS) spectra of the Si(001)-(2×1)/K and Si(001)-(2×1)/Cs surfaces have been measured for alkali-metal-atom coverages ranging from zero to saturation. Valence-band spectra and corresponding binding energy versus wave vector diagrams for the full-coverage Si(001)-(2×1)/K and Si(001)-(2×1)/Cs surfaces show that the two surfaces are semiconducting, in contrast to a generally accepted view of the one-dimensional and metallic alkali chain of the alkali/Si(001) systems. Plausible dispersions of surface-state bands are proposed for the full-coverage Si(001)-(2×1)/K and Si(001)-(2×1)/Cs surfaces. Normal-emission ARUPS spectra of outermost core levels of K and Cs have been found to be essentially invariant with alkali-metal-atom coverage in spite of large changes in work function. The effect of substrate doping on the ARUPS spectra has been examined.