Nonwetting of He-4 and dilute He-3-He-4 mixtures on Cs

For pure He-4 on Cs a nonwet phase exists below approximate to 2 K but for dilute He-3-He-4 mixtures the welting is reentrant. Measurements of the con tact angle with dilute mixtures of liquid helium on Cs can be explained in detail in terms of He-3 states together with ripplons at the Cs-He mixture interface, but it is impossible to account for the lower wetting temperatur es or contact angles with only He-3 states or ripplons. We discuss the infl uence of surface roughness of the Cs on the contribution of interface excit ations to the free energy and suggest that the variety of contact angles fo und with different samples of Cs is due mainly to their degree of roughness . (C) 2000 Elsevier Science B.V. All rights reserved.