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 accurate ly the surface and interface properties of liquid He-4 in the temperature r ange 0 < T < 3 K. We have used this functional to study the wetting propert ies of He-4 on the surface of alkali metals. In the case of adsorption on t he Cs surface, we find good agreement with experiments for both the low tem perature contact angle and the wetting transition temperature. At variance with the experimental results, we predict a wetting transition on the Rb su rface at T similar to 1.4 K. We believe that the disagreement with the expe rimental 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 s ubstrate roughness, which is known to affect the Rb surface, and whose effe ct would be to lower the wetting temperature. (C) 2001 Published by Elsevie r Science B.V.