WETTING PROPERTIES OF LIQUID-HELIUM ON RUBIDIUM METAL

Wetting properties of liquid helium on rubidium metal have been invest igated in the temperature range 1.0-1.7 K using a heat conduction meth od. The rubidium surface is found to be wetted under saturated vapor c onditions. Prewetting transitions have been observed for rather weak o ffsets from saturation, indicating that rubidium is close to the nonwe tting limit at T = 0 K. Presumably because of substrate inhomogeneitie s, the prewetting transitions are experimentally found to be continuou s and hysteretic. No evidence for the prewetting critical point has be en found up to 1.7 K. The prewetting line verifies a simple linear rel ation between the liquid-vapour surface tension and the two third powe r of the chemical potential offset, but does not conform quantitativel y to the simple model currently used.