Autoionization and energy-loss structures in Nb and Mo clean and oxygen-exposed surfaces

Autoionization features have been observed in Nb and Mo surfaces above the N23VV Auger lines. Similarly to 3d transition metals, they are interpreted as due to a coherent decay of the excited 4p electron and to a subsequent interference effect with the direct photoexcitation channel from the valence band. If the radial dependence of the 4d wavefunction does not vary strongly across the band, the line shape of the autoionization electron emission is expected to be similar to the core-energy loss result from 4p core levels. The correspondence between secondary electron emission and energy loss backscattering yield has been studied for both the clean and oxygen-exposed surfaces. A close similarity is found between the electron-induced phenomena observed above the N23VV Auger lines and the N23 core absorption. © 1989.