Nucleation of SolidHe4Interfaces between Grafoil and High-Pressure LiquidHe4

We report the continuous growth, on a microscopic scale, of solid ${\mathrm{He}}^4$ from superfluid ${\mathrm{He}}^4$ caused by its substrate interaction with Grafoil. The measurements indicate the presence of a surface solid layer whose thickness varies from 8 Å to more than 30 Å from the Grafoil substrate as the bulk solidification curve is approached. The results are in good agreement with a theory based on the van der Waals attraction between the ${\mathrm{He}}^4$ and the substrate.