The effects of a finite substrate-helium interaction and of the crystalline structure of a substrate potential on the liquid phase of a monolayer of helium are explored for models of three systems: helium physisorbed on a basal-plane surface of graphite; 4He adsorbed on graphite preplated by a close-packed layer of neon; and 4He adsorbed on graphite preplated by a close-packed layer of argon. The ground-state energy as a function of the areal density is calculated for each of these models by introducing a class of trial wave functions which have finite extent orthogonal to the substrate, possess the same translational symmetry as the substrate, and include short-range correlations between the helium atoms. The results for 4He on bare graphite are virtually identical with previous results for the model of 4He atoms in a two-dimensional structureless box, with very small quantitative differences. The indications for 3He on bare graphite are that the liquid is not self-bound. In contrast to the bare-graphite substrate, the other two substrates exert a strong influence on the liquid, substantially increasing the equilibrium density.
Title
Effects of crystalline substrate potentials on quasi-two-dimensional liquid helium
Novaco, A. D. and C. E. Campbell (1975). "Effects of crystalline substrate potentials on quasi-two-dimensional liquid helium." Physical Review B 11 (7): 2525–2534.