Hydrogen adsorption at room temperature on a clean (110) surface of a nickel single crystal is accompanied by reconstructive rearrangement of the surface metal atoms to form a (2times;1) surface structure. It is possible to remove this adsorbed hydrogen and obtain a planar surface by heating the crystal slightly above room temperature. A determination of the temperatures and equilibrium hydrogen pressures necessary to remove this adsorbed hydrogen yields an isosteric heat of adsorption of 1.2 eV.Oxygen displaces the hydrogen in the (2times;1) structure from the surface and results in the formation of the (1times;2) structure characteristic of adsorbed oxygen. This oxygen can be removed from the surface, however, by heating the crystal to 200deg;C in hydrogen.
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