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Ultraviolet photoemission spectra of nickel atoms vapor deposited on an amorphous carbon substrate show a characteristic energy-loss peak 6 eV below Ef for the full range of coverages from adsorbed nickel adatoms to bulk nickel. The quasiatomic excitation responsible for this energy-loss peak is the promotion of a nickel valence-shell electron to a $4p$ level in the ionic final state.
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Tibbetts et al. (1978) studied this question.
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