Abstract
The thermal desorption of CO from nickel surfaces has been used to follow the interaction of carbon with oxygen. The CO desorption spectrum subsequent to oxygen exposure of an initially clean nickel surface exhibits three principal peaks denoted as α, β 1, and β 2. The low-temperature a peak is believed to correspond to the desorption of molecularly adsorbed CO. The high-temperature β 2 peak is due to the desorption of CO formed by surface combination of dissociatively adsorbed oxygen and carbon diffusing from the crystal interior. The intermediate-temperature β 1 peak is also believed to be due to CO formed by combination of O and C at the surface. Evidence suggests that the surface carbon contributing to the β 1 peak arises from the segregation of carbon from the bulk to the surface before or during oxygen exposure. The β 1 peak is very sensitive to surface orientation and is, in particular, significantly enhanced as the degree of atomic surface roughness increases. These results are discussed in terms of preferential carbon segregation to surface defect sites.
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