Band structure and heat capacity of low-coverage helium films on noble-gas-plated graphite

Calculations are presented of the energy band structure of He4 atoms moving across the surface of a monolayer of Ar, Kr, or Xe adsorbed on graphite. The results are very sensitive to adsorbate density, allowing the possibility of experimentally varying the degree of He localization. From the dispersion relation, the density of states and low-coverage heat capacity are computed. In the case of Ar plating, agreement is obtained with the isosteric heat measurement of Lerner and Daunt. Speculation is made that the heat-capacity data of Crary et al. are influenced by Ar atoms on the second layer. In the case of Kr plating, satisfactory agreement is obtained with the data of Tejwani, Ferreira, and Vilches.