Abstract
The interaction of carbon and oxygen on Ni surfaces has been followed through observations of the thermal desorption of CO. Measurements have been made for surfaces of various orientations and for different coverages by sulphur. We have studied the reaction over a wide range of oxygen exposures. The CO desorption spectrum exhibits three principle peaks labelled α, β1 and β2. The low temperature α peak corresponds to molecularly adsorbed CO. The β1 peak is believed to be associated with surface defects and varies in a systematic way with average step density. We believe that it arises from CO formed from preferentially segregated carbon and surface oxygen. It is very sensitive to the coverage of adsorbed S. The high temperature β2 peak is due to the reaction of surface oxygen and carbon diffusing to the surface from the bulk. A diffusion model has been used to quantitatively interpret the β2 peak and yields an activation energy for interstitial carbon diffusion, in good agreement with previous independent experiments. The activation energy for desorption of CO in the β2 peak is independent of S coverage. The sources of the carbon and oxygen contributing to the different CO desorption peaks have been studied using controlled background pressures of 13C18O.
Original language | English |
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Pages (from-to) | 463-470 |
Number of pages | 8 |
Journal | Surface Science |
Volume | 152-153 |
Issue number | PART 1 |
DOIs | |
State | Published - Apr 1985 |
Externally published | Yes |
Funding
The authors wish to thank David Fowler for helpful discussions of results and equipment design. The crystals were skillfully prepared by B.F. Addis. The work was supported by the National Science Foundation, grant No. DMR-7926443.J .M.B. wishes to acknowledge the stimulating environment provided