Europhys. Lett.
Volume 76, Number 5, December 2006
Page(s) 877 - 883
Section Condensed matter: structural, mechanical and thermal properties
Published online 08 November 2006
Europhys. Lett., 76 (5), pp. 877-883 (2006)
DOI: 10.1209/epl/i2006-10366-3

Surface diffusion of hydrogen atoms on $\chem{Cu(111)}$ studied by optical diffraction from hydrogen density patterns formed on removable templates of xenon monolayers

Y. 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 $\chem{Cu(111)}$ 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 $\chem{Cu(111)}$ using the interference pattern of two coherent laser pulses. By following the evolution of hydrogen density gratings on $\chem{Cu(111)}$ from 153 to 183$\un{K}$ with linear optical diffraction, we found that the diffusion of hydrogen atoms on $\chem{Cu(111)}$ in this temperature range is the classical over-barrier hopping characterized by an activation energy barrier $E_{\ab{diff}} = 6.4\un{Kcal/mol}$ (or 279$\un{meV}$) and a pre-exponential factor $D_{0} = 2.0 \times 10^{ - 3}\un{cm^{2}/s}$. Based on the potential model proposed by Basdescu and coworkers for hydrogen on $\chem{Ni(111)}$, the WKB tunneling coefficient between the first vibrational excited states of a hydrogen adatom on $\chem{Cu(111)}$ is expected to be at least one order of magnitude smaller than that on $\chem{Ni(111)}$, indicating that the classical over-barrier hopping of hydrogen atoms could directly cross over to under-barrier tunneling between ground states on $\chem{Cu(111)}$.

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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