Thermodynamic and Neutron-Diffraction Studies of H2 and D2 Multilayers Physisorbed on Graphite

  • H. Wiechert
Part of the NATO ASI Series book series (NSSB, volume 257)

Abstract

The evolution of physisorbed films from two-dimensional (2D) to bulk behavior is a topic of high current interest.1 In this context the behavior of the quantum systems H2, HD and D2 is of particular relevance because of the following reasons:
  1. 1.

    Due to the strong influence of the quantum zero-point energy the hydrogen isotopes are highly compressible. This leads to strongly compressed monolayers2,3 before further layer condensation occurs. This property makes these systems significant for the exploration of conditions of multilayer growth. It is generally believed,1,4–6 that the incompatibility between the adsorbate and bulk lattice structures gives rise to lateral strains between the overlayers, which may cause reentrant incomplete wetting phenomena7 in the weakly physisorbed quantum systems. Thus the behavior of the first few layers next to the substrate is of crucial importance for the character of the multilayer growth.

     
  2. 2.

    The phase diagrams and structures of hydrogen isotope multilayers adsorbed on graphite are unknown so far. Recently, detailed specific-heat studies8–12 mapped out the phase diagrams of the monolayers, and with neutron diffraction2,3,12–17 and LEED17,18 the structures of the observed phases were identified. At low coverages these systems exhibit a commensurate (√3×√3) R30° phase2,3 due to the strong influence of the substrate corrugation potential, and undergo a commensurate-incommensurate (C-IC) transition via a sequence of different domain-wall phases8–18 to an equilaterally spaced triangular compressed incommensurate phase at higher coverages. First exploratory neutron-diffraction measurements of D2 multilayers19 found common oblique bi- and trilayer structures. A recent study of the multilayer growth of H2 adsorbed on MgO20 discovered the occurrence of a conventional van der Waals phase diagram including triple and critical points in the second layer and a succession of layering transitions at higher coverages.

     
  3. 3.

    The weakly bound states of hydrogen multilayers on substrates may be close to the limiting case where a quantum system at low temperatures condenses as a liquid rather than as a solid.21 H2 is a Bose particle and is expected to undergo a Bose-Einstein condensation to a superfluid phase provided the solidification can be suppressed to temperatures below 6.6 K22 and probably even lower in a real system.23 For the second layer of H2 on MgO a triple line at 7.2 K was found,20 which is still too high for a superfluid transition. The question remains: Do the molecules in the second layer of H2 on graphite condense into localized states?

     

Keywords

Methane Graphite Carbide Total Heat Foam 

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References

  1. 1.
    For recent reviews, see, e.g.: J. G. Dash, in: “Solvay Conference on Surface Science”, F. W. de Wette, ed., Springer Verlag, Berlin (1988), p. 142Google Scholar
  2. S. Dietrich, in: “Phase Transitions and Critical Phenomena”, Vol. 12, C. Domb and J. L. Lebowitz, eds., Academic Press, London (1988), p. 1; and references cited therein.Google Scholar
  3. 2.
    M. Nielsen. J. P. McTague. and W. Ellenson, J Phys. (Paris) Colton. 38: C 4–10 (1977).Google Scholar
  4. 3.
    M. Nielsen, J. P. McTague, and L. Passell, in: “Phase Transitions in Surface Films”, J. G. Dash and J. Ruvalds, eds., Plenum, New York (1980), p. 127.Google Scholar
  5. 4.
    R. J. Muirhead, J. G. Dash, and J. Krim, Phys. Rev. B29: 5074 (1984).ADSCrossRefGoogle Scholar
  6. 5.
    D. A. Huse, Phys. Rev. B29: 6985 (1984).MathSciNetADSCrossRefGoogle Scholar
  7. 6.
    F. T. Gittes and M. Schick, Phvs. Rev. B30: 209 (1984).ADSCrossRefGoogle Scholar
  8. 7.
    M. Bienfait, J. L. Seguin, J. Suzanne, E. Lerner, J. Krim, and J. G. Dash, Phys. Rev. B29, 983 (1984).ADSGoogle Scholar
  9. 8.
    H. Wiechert and H. Freimuth, in: “ Proc. 17th Intern. Conf. on Low Temp. Phys. LT-17”, U. Eckern et al., eds., North-Holland, Amsterdam (1984), p. 1015.Google Scholar
  10. 9.
    H. Freimuth and H. Wiechert, Surf. Sci. 162: 432 (1985).ADSCrossRefGoogle Scholar
  11. 10.
    F. C. Motteler and J. G. Dash. Phys. Rev. B31: 346 (1985)ADSCrossRefGoogle Scholar
  12. F. C. Motteler, Ph. D. dissertation, University of Washington (1986).Google Scholar
  13. 11.
    H. Freimuth and H. Wiechert. Surf. Sci. 178: 716 (1986).ADSCrossRefGoogle Scholar
  14. 12.
    H. Freimuth, H. Wiechert, and H. J. Lauter. Surf. Sci. 190: 548 (1987).ADSCrossRefGoogle Scholar
  15. 13.
    H. Wiechert, H. Freimuth, H. P. Schildberg, and H. J. Lauter, Iapn. J Appl. Phys. 26, Suppl. 26–3: 351 (1987).Google Scholar
  16. 14.
    H. P. Schildberg, H. J. Lauter, H. Freimuth, H. Wiechert, and R. Haensel, Iapn. J. Appl. Phys. 26, Suppl. 26–3: 345 (1987).Google Scholar
  17. 15.
    H. J. Lauter, in: “Phonons 89”, S. Hunklinger, W. Ludwig, and G. Weiss, eds., World Scientific, Singapore (1990), p. 871.Google Scholar
  18. 16.
    H. Freimuth, H. Wiechert. H. P. Schildberg, and H. J. Lauter, Phys. Rev. B42: 587 (1990).ADSCrossRefGoogle Scholar
  19. 17.
    J. Cui, S. C. Fain, H. Freimuth, H. Wiechert, H. P. Schildberg, and H. J. Lauter, Phys. Rev. Lett. 60: 1848 (1988); 2704 (1988).CrossRefGoogle Scholar
  20. 18.
    J. Cui and S. C. Fain, Phys. Rev. B39: 8628 (1989).ADSCrossRefGoogle Scholar
  21. 19.
    H. P. Schildberg, H. J. Lauter, H. Freimuth, H. Wiechert, and R. Haensel, Iapn. J. Appl. Phys. 26, Suppl. 26–3: 343 (1987).Google Scholar
  22. 20.
    J. Ma, D. L. Kingsbury, F. Liu, and O. E. Vilches, Phys. Rev. Lett. 61: 2348 (1988).ADSCrossRefGoogle Scholar
  23. 21.
    X. Z. Ni and L. W. Bruch, Phys. Rev. B33: 4584 (1986).ADSCrossRefGoogle Scholar
  24. 22.
    V. L. Ginzburg and A. A. Sobyanin, IETP Lett. 15: 242 (1972).ADSGoogle Scholar
  25. 23.
    H. J. Maris. G. M. Seidel, and T. E. Huber, J. Low Temp. Phvs. 51: 471 (1983).Google Scholar
  26. 24.
    R. J. Birgeneau, P. A. Heiney, and J. P. Pelz, Physica 109/110 B: 1785 (1982).Google Scholar
  27. 25.
    H. P. Schildberg and H. J. Lauter Surf. Sci. 208: 507 (1989).ADSCrossRefGoogle Scholar
  28. 26.
    D. M. Zhu, D. Pengra, and J. G. Dash, Phys. Rev. B 37: 5586 (1988).ADSCrossRefGoogle Scholar
  29. 27.
    D. M. Zhu and J. G. Dash, Phys. Rev. B 38: 11673 (1988).ADSCrossRefGoogle Scholar
  30. 28.
    H. K. Kim and M. H. W. Chan, Phys. Rev. Lett. 53: 170 (1984).ADSCrossRefGoogle Scholar
  31. 29.
    M. J. de Oliveira and R. B. Griffiths, Surf. Sci. 71: 687 (1978).Google Scholar
  32. 30.
    M. P. Nightingale, W. F. Saam, and M. Schick, Phys. Rev. B 30: 3830 (1984).ADSCrossRefGoogle Scholar
  33. 31.
    M. S. Pettersen, M. J. Lysek, and D. L. Goodstein, Phys. Rev. B 40: 4938 (1989).ADSCrossRefGoogle Scholar
  34. 32.
    J. Ma, T. S. Sullivan, and O. E. Vilches, Jann., Appl. Phys. 26, Suppl. 26–3: 263 (1987).Google Scholar
  35. 33.
    M. Nielsen, Phys. Rev. B 7: 1626 (1973).ADSCrossRefGoogle Scholar
  36. 34.
    K. Carneiro, L. Passell, W. Thomlinson, and H. Taub, Phys. Rev. B 24: 1170 (1981).ADSCrossRefGoogle Scholar
  37. 35.
    J. M. Phillips and C. D. Hruska, Phys. Rev. B 39: 5425 (1989).ADSCrossRefGoogle Scholar

Copyright information

© Plenum Press, New York 1991

Authors and Affiliations

  • H. Wiechert
    • 1
  1. 1.Institut für PhysikJohannes Gutenberg-UniversitätMainzGermany

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