SPECTROSCOPIC EVIDENCE FOR CARBON CARBON BONDING IN CARBIDIC LAYERS ON METALS

We examine previously reported ultraviolet photoelectron, CK electron energy loss, and CKVV Auger spectroscopic data from "carbidic" layers formed at temperatures between 500 and 650 K on Ni(100) and Ni(111). The "carbidic" layers studied were made from either CO or C2H4 exposure to the metal surface. These data indicate that significant amounts of carbon-carbon bonding exists on the surface in addition to the carbon-metal bonding with the substrate, revealing the presence of chemisorbed species, such as C2, and maybe even C3, etc. Quantitative interpretations of the Auger data indicate that 20 to 30% of the total electron density has carbon-carbon bonding character. Observed changes in the spectra obtained from different surfaces or at different coverages are accounted for by variations in the fraction of carbon-carbon bonding character.