Two-dimensional condensation of potassium on Ag(001)

Temperature- and coverage-dependent soft-x-ray photoemission and photoabsorption studies on potassium-covered Ag(001) surfaces demonstrate the formation of potassium two-dimensional compressed islands, even at coverages far below saturation. The expected disperse-overlayer structure is metastable, and is irreversibly transformed into the compressed phase at higher temperature. These results indicate that the short-range attractive adsorbate-adsorbate interaction overcomes the electrostatic repulsion and the surface-corrugation potential, and that the adsorbate-substrate charge transfer is insignificant, supporting recent theoretical studies.