Surface diffusion of hydrogen atoms on studied by optical diffraction from hydrogen density patterns formed on removable templates of xenon monolayersY. Y. Fei and X. D. Zhu
Department of Physics, University of California - Davis, CA 95616, USA
received 16 July 2006; accepted in final form 13 October 2006
published online 8 November 2006
We formed grating-like patterns of hydrogen adatom density on by using complementary patterns of xenon adatom density as the template. The template was pre-formed by laser-induced thermal desorption of a Xe monolayer on using the interference pattern of two coherent laser pulses. By following the evolution of hydrogen density gratings on from 153 to 183 with linear optical diffraction, we found that the diffusion of hydrogen atoms on in this temperature range is the classical over-barrier hopping characterized by an activation energy barrier (or 279) and a pre-exponential factor . Based on the potential model proposed by Basdescu and coworkers for hydrogen on , the WKB tunneling coefficient between the first vibrational excited states of a hydrogen adatom on is expected to be at least one order of magnitude smaller than that on , indicating that the classical over-barrier hopping of hydrogen atoms could directly cross over to under-barrier tunneling between ground states on .
68.43.Jk - Diffusion of adsorbates, kinetics of coarsening and aggregation.
78.68.+m - Optical properties of surfaces.
81.15.-z - Methods of deposition of films and coatings; film growth and epitaxy.
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