Specific heat near the superfluid transition of a 0.9869 mu m He-4 film

We report measurements of the specific heat of He-4 near the superfluid tra nsition while confined between silicon wafers at 0.9869 mum separation. The se data are analyzed to check on the behavior expected from correlation-len gth scaling. Comparison is also made with other data for planar confinement , as well as data for cylindrical confinement. These represent different lo wer-dimensional crossovers. We find that the present data scale very well a bove the bulk transition temperature, and in the region immediately below i t. Near the specific heat maximum however, the data for planar confinement do not collapse on a universal curve. We compare these results with specifi c theoretical scaling functions. In particular we find that on the normal s ide, and for large enough values of the scaling variable, one can describe the data well using the concept of the surface specific heat. The locus of the data in this region agrees well with most recent theoretical calculatio ns.