The CKVV Auger line shapes of ethylene chemisorbed on Ni(100) at 100, 250, 300 and 600 K are reported and consistently interpreted. These line shapes are representative of π-bonded ethylene (C2H4(a)) at 100 K, σ-bonded vinyl (CHCH2(a)) at 250 K, a mixture of ethynyl (CCH(a)), methylidyne (CH(a)) and di-σ-bonded acetylene (HCCH(a)) at 300 K, and carbidic carbon (C(a)) at 600 K on the surface. The Auger line shape of graphitic carbon adlayers on Ni is also interpreted. The line shapes are found to consist of adsorbate-adsorbate, adsorbate-substrate, and substrate-substrate components, which are denoted by the final location of the two holes created by the Auger process. The adsorbate-adsorbate component, for the C2 chemisorbed species, reflects primarily the valence density of states of ethylene and shows negligible hole-hole correlation effects due to electron transfer from the metal. This is in contrast to the graphitic adlayer where the adsorbate-adsorbate component has the same line shape as bulk graphite and exhibits significant correlation effects. The adsorbate-substrate and substrate-substrate components seen in all of the line shapes directly reflect the adsorbate-substrate π or σ bonding character, and the extent of screening via charge transfer from the metal to the core excited adsorbate.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry