A simple doser for atomic hydrogen is described. It basically consists of a tungsten capillary which on the outlet is heated by electron bombardment to 1800–2000 K. This temperature is sufficient to achieve nearly total H2 dissociation under relevant working pressures. The performance of the atomic hydrogen source was tested by H adsorption studies on Cu(110). The saturation coverage on this surface could be achieved with a nominal exposure which was smaller by a factor of ∼10−3 as compared to conventional methods of dissociation on a hot filament. The higher efficiency of the present H source greatly reduces the risk of sample contamination.

The sticking coefficient of atomic hydrogen at T G = 1815 K on a Cu(l 10) surface has been determined to be 18%. In addition to the buildup of a chemisorption layer the absorption of atomic H into subsurface sites is observed. The subsurface sites are thermally less stable than the chemisorption sites. Model calculations for the phononic energy transfer and estimates for the parallel momentum transfer as well as for electron-hole pair excitation indicate that the first two mechanisms dominate the accommodation process.

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