The adsorption of He-4 on alkali metal surfaces from finite-temperature density functional calculations

We have constructed a non-local density-functional which describes accurately the surface and interface properties of liquid He-4 in the temperature range 0 < T < 3 K. We have used this functional to study the wetting properties of He-4 on the surface of alkali metals. In the case of adsorption on the Cs surface, we find good agreement with experiments for both the low temperature contact angle and the wetting transition temperature. At variance with the experimental results, we predict a wetting transition on the Rb surface at T similar to 1.4 K. We believe that the disagreement with the experimental results for the He/Rb system is due either to an inaccuracy of the fluid-substrate potential used in our calculations or the consequence of substrate roughness, which is known to affect the Rb surface, and whose effect would be to lower the wetting temperature.