NONWETTING AND STICKING OF ARGON ON ALKALI-METAL SURFACES

We investigated the adsorption of argon on alkali metals (K,Cs) grown on Ru(001) by temperature programmed desorption (TPD). TPD spectra are characteristic for non-wetting, and the coverage dependence of the desorption energy can be explained in a simple droplet model. Nevertheless, the initial sticking coefficient s0 is not affected by nucleation and is thus determined by the interaction of Ar atoms with the alkali metal surface. The s0 values can be understood quantitatively within a semiclassical forced oscillator model with reasonable interaction parameters. For Ar/Cs, the measured gas temperature dependence gives access to the combined Morse potential parameters D and alpha, although they cannot be determined independently. Quantum effects in the sticking [1] are expected for Ar/K.