Adsorption of3He and4He on copper and on argon-coated copper below 20 K

Abstract

Measurements have been made of adsorption isotherms of3He and of4He on copper and on a monolayer of argon deposited on copper in the temperature range 6.18–18.55 K and in the pressure range 0.25 to 75 Torr. From these many isotherms, calculations have been made of the isosteric heat of adsorptionQst/R. In the limit of zero coverage on the argon monolayerQst/R=76±2 K for3He and 76±2 K for4He. For adsorption on the bare copper,Qst/R is difficult to extrapolate to zero coverage, but it probably lies (for both3He and4He) between 135 and 165 K. At theoretical monolayer helium coverage,Qst/R=44±2 K for3He on the argon monolayer and 47±2 K for4He. At theoretical monolayer helium coverage on the bare copper,Qst/R=61±4 K for3He and 77±5 K for4He. The results are compared with theoretical evaluations for helium adsorbed on an argon monolayer and with some previous experimental data, and the agreement is found to be fair. All the data are summarized in tables. Finally, a review is given of evaluations, including those from this work, of the monolayer capacity of3He and4He on the substrates studied.