Binding of carbon atoms at a stepped−Ni surface

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Abstract
We have studied the equilibrium segregation of carbon to a stepped surface of nickel, Ni[S] [7(100) × (1̄33)] using Auger electron spectroscopy and LEED. At temperatures below 640 K diffuse p (2×2) structures were observed to form and progressively sharpen as the temperature was lowered. The p (2×2) spots were split, indicating ordering between terraces. The surface coverage of carbon vs temperature was well described by a Langmuir model, but with three distinct heats of segregation ΔEseg = −0.82 eV for ϑ?1/3, ΔEseg = −0.51 eV for 1/3 <ϑ<2/3, and ΔEseg = −0.37 eV for 2/3?ϑ≲1. The ratio of integrated Auger current to the peak−peak value on the derivative spectrum changes abruptly at ϑ?1/3, 2/3, indicating a change in chemical bonding. These results are interpreted in terms of terrace dimensions, and provide information to complement experiments performed on Ni(100) surfaces in the same temperature and doping range.

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