Submonolayer Isotopic Mixtures of Helium Adsorbed on Grafoil

  • S. V. Hering
  • D. C. Hickernell
  • E. O. McLean
  • O. E. Vilches


Monolayers or submonolayers of helium adsorbed on different substrates have been studied for several years. Heat capacity signatures for He on rouge,1 Vycor,2 and bare and rare-gas-plated copper3–5 resemble those of two-dimensional (2D) Debye systems. Only recently measurements done on a commercially available variety of graphite, Grafoil,§ have given results that can be compared to 2D quantum and classical gases.6 Several prominent features have been reported in the range between 1/4 and 2/3 monolayer, mainly: (a) classical k/atom specific heats at 4°K; (b) peaks around 1.2°K appearing only for bosons (4He) at the lower coverages, assumed due to condensation induced by weak substrate lateral fields6,7; (c) peaks around 3°K occurring for coverages at which a well-defined fraction of the Grafoil lattice hexagons x G is occupied by He atoms (x G = 1/4 and x G = 1/3); (d) spin-ordering effects appearing for 3He at very low temperatures.8 Comparisons have been made with the properties of liquid and solid 3He and 4He, and it appears that 2D films on Grafoil have properties corresponding to those of the three-dimensional (3D) systems (see, e.g., a recent report on the melting line).9


Mole Fraction Excess Entropy Pure Isotope Specific Heat Data Excess Specific Heat 
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Copyright information

© Springer Science+Business Media New York 1974

Authors and Affiliations

  • S. V. Hering
    • 1
  • D. C. Hickernell
    • 1
  • E. O. McLean
    • 1
  • O. E. Vilches
    • 1
  1. 1.Department of PhysicsUniversity of WashingtonSeattleUSA

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