Novel wetting behavior of 4He on cesium.

Abstract

We have measured $^{4}\mathrm{He}$ adsorption isotherms on a cesium substrate above and below ${\mathit{T}}_{\ensuremath{\lambda}}$ using a quartz-microbalance technique. The results show that the cesium surface remains dry until the pressure almost reaches the saturated vapor pressure. At liquid-vapor coexistence, however, the wetting film continuously thickens to more than 30 layers. Below ${\mathit{T}}_{\ensuremath{\lambda}}$, the film at coexistence is superfluid. Above ${\mathit{T}}_{\ensuremath{\lambda}}$, we resolve a feature in the isotherm just below saturated vapor pressure which is characteristic of a prewetting transition.