Experimental study of the growth of liquid 4He films on graphite

We report experiments with superfluid 4He films physisorbed on graphite which indicate a continuous growth of the film up to at least 25 layers. The growth of the film is monitored by the decreasing third-sound resonance frequency of an annular resonator made out of graphite fibers; such a resonator overcomes problems of capillary condensation and interference from ordinary sound in the helium vapor. Measurements have been performed from 1.25 K to as low as 0.35 K