Zero-point Surface Phonons - Effect On Wetting

The recently observed behavior of helium films adsorbed on alkali metal surfaces has confirmed earlier ideas about wetting and prewetting transitions. However, a quantitative discrepancy between the predicted and observed wetting temperature suggests that a reexamination of the energetics of adsorbed helium films is required. We show how the zero point phonon energy of an alkali-vapor interface can dramatically change the wetting properties of these substrates, in accord with experiment. We investigate the dependence on the exposed facet of the crystal surface. For Rb and Cs, the (110) face is predicted to be wet at zero temperature while the (100) face is not. An isotope effect is also predicted.