Adsorption of sodium and potassium on a gold(100) surface: An example of alkali-metal-induced deconstruction

We have studied the interaction of Na and K with a (5×20) reconstructed Au(100) surface between 130 and 1150 K using low-energy-electron-diffraction (LEED), x-ray-photoelectron spectroscopy (XPS), work-function change (ΔΦ), and thermal-desorption spectroscopy (TDS) measurements. Our results indicate a strong temperature dependence of the interaction phenomena: At 300 K, we find for both Na and K adsorption the lifting of the inherent (5×20) reconstruction at a critical coverage ${\mathrm{\Theta }}_{\mathrm{crit}}$≊0.2 ML, and, at somewhat larger Θ, a thermally activated transformation to a (likewise reconstructed) (1×2) phase of the missing-row (MR) type. Higher coverages lead to different LEED structures depending on the alkali metal and the deposition temperature. All structural changes are sensitively mirrored in the ΔΦ-Θ relations, which reveal intermediate work-function maxima right at ${\mathrm{\Theta }}_{\mathrm{crit}}$. These maxima are superimposed on the typical descending ΔΦ-Θ curves usually observed with alkali-metal adsorption on metal surfaces (Δ${\mathrm{\Phi }}_{\mathrm{m}\mathrm{a}\mathrm{x},\mathrm{N}\mathrm{a}}$=-1.9 eV; Δ${\mathrm{\Phi }}_{\mathrm{m}\mathrm{a}\mathrm{x},\mathrm{K}}$=-2.6 eV). At 130 K, the formation of the (1×2) MR reconstructed phases cannot be observed anymore, and accordingly no intermediate ΔΦ maxima appear.