Studies of the Electron Spectrum with Reference to the Clean Surfaces of Iron, Cobalt and Nickel and Their Subsequent Exposure to Oxygen.

The electron spectrum of the clean and oxygen exposed (110) surfaces of the transition metals of Fe, Co and Ni have been studied. This has included consideration of the core-valence-valence (CVV) Auger emission, autoionisation electron emission, resonant photoemission, the hole-hole Coulomb interaction energy U_{rm eff}, the electron loss spectra, the core loss spectra and the reflected extended electron energy loss fine structure (REELFS). The M_{2,3}VV Auger and 3p core loss spectra for clean and oxygen-exposed surfaces of the transition metals Fe, Co and Ni have been studied. All the peaks observed in the Auger spectra are accounted for in terms of both atomic and bandlike M _{2,3}M_{4,5 }M_{4,5} transitions and an autoionization emission involving the decay of a localized exicted state. For the clean surfaces the localized excitation and subsequent deexcitation by autoionization emission is considered, within a quasiatomic model, to be 3p^63d^{ rm n} 3p^53d ^{rm n}d^ {*} 3p^63d ^{rm n-1} + el. However, upon oxidation of these surfaces, the splitting observed in the 3p core loss spectra and the energy of the observed autoionization peaks indicate changes in the nature of the excitation due to the chemical environment. This is contrary to the accepted notion for such quasiatomic processes, which are considered essentially unaffected by the chemical environment. Further, for these oxidized surfaces, the observed autoionization features are shown to be associated with the excitation of 3p electrons to a localized state at the bottom of the conduction band as opposed to the empty d states at the top of the valence band. Arguing from Auger, autoionisation and published resonant photoemission results it is suggested the U _{rm eff} does not alter appreciably on oxidation. The use of XPS binding energies in Auger experiments is critically evaluated. The REELFS structure discovered beyond the shallow M_{2,3} core loss edge has been treated analogously to EXAFS and shown to have potential as an economical surface technique.