Hamilton, Jeffrey J. and Goodstein, David L. (1983) Thermodynamic study of methane multilayers adsorbed on graphite. Physical Review B, 28 (7). pp. 3838-3848. ISSN 0163-1829 http://resolver.caltech.edu/CaltechAUTHORS:HAMprb83
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We have made thermodynamic measurements of the properties of methane adsorbed on graphite in the ranges, roughly, 1—6 molecular layers and 64—105 K. Interpreting the results in the context of current models, we tentatively conclude that layer by layer, critical points occur at approximately constant temperature around 78 K. Extrapolation of this observation would imply a roughening transition in bulk solid methane at about that temperature. We also observe a line of melting transitions that extends from the bulk triple point, Tt=90.7 K, into the multilayer region at nearly constant temperature. The transition in films of less than ∼5 layers does not appear to be first order, but it is associated with a change in entropy. The change in entropy gradually diminishes, vanishing entirely at about 2 layers. It is not clear how the transition closes, but a number of possibilities is discussed.
|Additional Information:||©1983 The American Physical Society Received 18 March 1983 We are grateful to Milton W. Cole, Joseph E. Avron, Michael Wortis, and Michael S. Pettersen for many stimulating and fruitful discussions. We would also like to thank André Thomy for sending us his data, and Michael P. Dowell of Union Carbide Corporation for providing us with noncommercial samples of Grafoil. This work was supported in part by a U.S. Department of Energy grant DE-AM03-76SF00767.|
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