The Nonwetting Behavior of Dilute 3He-4He Mixtures on Cs

We present evidence for ³ He interfacial bound states at the Cs-liquid He interface and show their influence on the interfacial free energies and the nonwetting behaviour of dilute ³ He- ⁴ He mixtures on Cs. The bound state energy and effective mass for the ³ He atoms at this interface are determined and found to be in good agreement with theoretical predictions. From the temperature dependence of the contact angle, direct evidence for a first order wetting transition at the lower wetting temperature is found. A detailed model is presented for the Cs-He mixture interface free energy and the contact angle and this model is shown to be in excellent agreement with the measurements. There is a short discussion on hysteresis and the thin film state. Finally it is emphasised that the large measured contact angles are only consistent with ³ He bound states together with ripplons at the Cs-He mixture interface