Grating-like patterns of H adatom density were formed on Cu(111) by using complementary patterns of Xe adatom density as a template. The template was pre-formed by laser-induced thermal desorption of a Xe monolayer on Cu(111) using the interference pattern of 2 coherent laser pulses. By following the evolution of H density gratings on Cu(111) from 153 to 183K with linear optical diffraction, it was found that the diffusion of H atoms on Cu(111) within this temperature range involved classical over-barrier hopping, described by:

D (cm2/s) = 2.0 x 10-3 exp[-0.279(eV)/kT]

Based upon a potential model proposed for H on Ni(111), the WKB tunneling coefficient between the first vibrational excited states of a H adatom on Cu(111) was expected to be at least an order of magnitude smaller than that on Ni(111); indicating that the classical over-barrier hopping of H atoms could directly cross over to under-barrier tunneling between ground states on Cu(111).

Surface Diffusion of Hydrogen Atoms on Cu(111) Studied by Optical Diffraction from Hydrogen Density Patterns Formed on Removable Templates of Xenon Monolayers. Y.Y.Fei, X.D.Zhu: Europhysics Letters, 2006, 76[5], 877-83