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Near-equilibrium desorption of helium films

Weimer, M. and Housley, R. M. and Goodstein, D. L. (1987) Near-equilibrium desorption of helium films. Physical Review B, 36 (10). pp. 5199-5214. ISSN 0163-1829.

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The thermal desorption of helium films in the presence of their equilibrium vapor is studied experimentally for small but rapid departures from ambient temperature. The results are analyzed within the framework of a quasithermodynamic phenomenological model based on detailed balance. Under the usual experimental conditions, isothermal desorption at the temperature of the substrate is a general prediction of the model which seems to be substantiated. For realistic adsorption isotherms the time evolution of the net desorption flux nevertheless appears to be governed by a highly nonlinear equation. In such circumstances, a number of characteristic relaxation times may be identified. These time scales are distinct from, and in general unrelated to, the coverage-dependent mean lifetime of an atom on the surface. To characterize the overall nonlinear evolution towards steady state, a global time scale, defined in terms of both initial- and steady-state properties, is introduced to summarize the experimental data. Internal evidence suggests a criterion for judging when collisions among desorbed atoms are unimportant. When this condition is satisfied, data for near-equilibrium desorption agree well with the predictions of the model. Combining our results with earlier data at higher substrate temperatures and different ambient conditions, the overall picture is consistent with scaling properties implied by the theory. We show that the values of the parameters deduced from a Frenkel-Arrhenius parametrization of the global relaxation times, as well as a variety of other aspects of desorption kinetics, are actually consequences of the shape of the equilibrium adsorption isotherm.

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Additional Information:©1987 The American Physical Society Received 23 March 1987 This work was supported by the Office of Naval Research (ONR) Contract No. N00014-80-C-0447 and U.S. Department of Energy Contract No. DE-FG03-85ER45192. One of us (M.W.) especially wishes to thank Dr. G. John Dick, of the California Institute of Technology Low Temperature Physics Laboratory, for several timely and illuminating discussions. The technical assistance of Mr. Edward Boud is also gratefully acknowledged.
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Deposited On:27 Nov 2006
Last Modified:26 Dec 2012 09:18

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