Theoretical support to the double-layer model for potassium adsorption on the Si(001) surface

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Abstract
K adsorption on the Si(001)-2×1 surface is studied by first-principles molecular dynamics based on a norm-conserving pseudopotential. The theoretically optimized structure for full coverage (Θ=1.0) agrees fairly well with the double-layer model analyzed by x-ray photoelectron diffraction. At Θ=0.5, the configuration with K adsorbed along the trough is more stable than the Levine model. The mean desorption energies for the two peaks in the thermal desorption spectrum are well accounted for by the present calculation. The calculated work-function change also agrees quantitatively with the observed one. Based on these analyses, it is concluded that the double-layer model should be appropriate for the saturation coverage of K on the Si(001) surface.