Self-consistent measurement of the adsorption of He on Cu, CO2, Ar, and Ne

Abstract

The chemical potentials as a function of He coverage have been determined from He adsorption isotherms measured at 1.72 K for the following thick substrates: Ne, Ar, and CO2-plated Cu, and bare Cu. The adsorption isotherm data were analyzed self-consistently using the modified Brunauer-Emmett-Teller method for low coverages and the Frenkel-Halsey-Hill vapor pressure relation at high coverages. The analysis establishes the surface area, chemical potential constant, Γ=−μd3, and capacity increases and heats of adsorption of the first and second monolayers of He for each adsorbent. The measured chemical potentials follow the expected inverse-cube law for coverages greater than 2.5 layers, but differ substantially for smaller coverages. We use results of the isotherm analysis to interpret measurements of third sound velocities, and to make precision measurements of the He inert (nonsuperfluid) layer coverages on these substrates