Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory

A. S. Foster, T. Trevethan, and A. L. Shluger
Phys. Rev. B 80, 115421 – Published 17 September 2009


Using periodic density functional theory, we calculate the structure and migration energies of fluorine vacancies and interstitials in the bulk and at the stoichiometric bulk-truncated surface of three alkali-earth fluorides: CaF2, SrF2, and BaF2. We then study the adsorption of water and hydrogen, in both molecular and dissociated form, at the ideal surface, and at neutral and charged vacancies in the surface and subsurface layers. The results demonstrate that in nearly all cases molecular adsorption is strongly favored. For the most probable configurations on the surfaces, we also studied the migration paths and barriers, and found that water is highly mobile on the surface, even when adsorbed at defects. In general, CaF2 and SrF2 show similar behavior with respect to water, while adsorption energies and migration barriers for BaF2 are smaller. Finally, we discuss our results in the context of recent experimental Atomic Force Microscopy studies on CaF2 and compare to calculations on other insulating surfaces.

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  • Received 27 March 2009


©2009 American Physical Society

Authors & Affiliations

A. S. Foster1,2, T. Trevethan3,4, and A. L. Shluger3,4

  • 1Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, 02015 Helsinki, Finland
  • 2Department of Physics, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland
  • 3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
  • 4WPI-AIMR Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan

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Vol. 80, Iss. 11 — 15 September 2009

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