AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuA

Paper SS1-TuA10
Adsorption Dynamics and Desorption Kinetics of Argon and Methane on MgO(100)

Tuesday, November 5, 2002, 5:00 pm, Room C-108

Session: Ultrafast Phenomena & Dynamics at Surfaces
Presenter: Z. Dohnálek, Pacific Northwest National Laboratory
Authors: Z. Dohnálek, Pacific Northwest National Laboratory
R.S. Smith, Pacific Northwest National Laboratory
B.D. Kay, Pacific Northwest National Laboratory
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The adsorption dynamics and desorption kinetics of Ar and CH@sub 4@ on MgO(100) are studied using a combination of molecular beam scattering and temperature programmed desorption (TPD). Both Ar and CH@sub 4@ exhibit an initial trapping probability that de creases dramatically with increasing kinetic energy and is independent of incident angle indicating adsorption is a barrier-less process obeying total energy scaling. The trapping probability for both adsorbates increases roughly linearly with the increa s ing coverage in the first layer. Such behavior can be described by a simple model involving constant but different trapping probabilities on clean and adsorbate covered MgO(100) with fast intra-layer diffusion leading to preferential filling of the bar e M gO(100). Analogous behavior is observed for trapping on the second and third layers and indicates layer-by-layer growth of the adsorbate overlayer with layer dependent trapping probabilities. Analysis of the TPD spectra yields desorption energies of 8.5 a nd 13 kJ/mole for Ar and CH@sub 4@, respectively in agreement with previous measurements and theoretical calculations. The total energy scaling observed for the initial trapping of Ar and CH@sub 4@ on MgO(100) is in sharp contrast with the normal en er g y s caling previously observed for these species on Pt(111). These differences indicate that the adsorbate-substrate interaction is laterally smooth on Pt(111) and highly-corrugated on MgO(100). Pacific Northwest National Laboratory is a multiprogram National Laboratory operated for the Department of Energy by Battelle under Contract DE-AC06-76RLO 1830.