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The growth of solid 4He on graphite from the superfluid phase is known to occur at pressures well below the bulk solidification point. The number of adsorbed layers increases with pressure and the solid growth undergoes non-continuous layer-by-layer growth at low temperature. We have studied this growth using the torsional oscillator method for isotherms down to 0.1 K. In contrast with simple layer-by-layer growth scenarios, our evidence suggests that the growth of adsorbed solid 4He is more complex and less solid is present on the graphite substrate at low temperature.

The thermal conductivity between the 3He solid films and the graphite substrate was measured by the relaxation method between 100 μK and 1 mK. The areal-density depedence of the thermal conductivity shows behavior similar to that of the exchange frequency J both in the submonolayer and in the second layer. These facts indicate that heat is transferred by magnetic mechanisms in the 3He solid film itself. They also imply that the 3He solid film is thermally connected with the graphite substrate only at some local spots.