Appearance potential study of N4,5-level of light rare earth metals and their oxides

Appearance potential spectroscopy (APS) probes the binding energy of core levels and local conduction band states of solid surfaces. Soft X-ray APS (SXAPS) and Auger electron APS (AEAPS) respectively measure the differential X-ray fluorescence and secondary electron yields as a function of incident electron energy. We have obtained the N_4,5-level SXAPS and AEAPS spectra of La, Ce, Pr, Nd and Sm metals and their oxides. The N_4,5-level AEAPS studies of these metals have not been reported previously. The comparison of the two spectra shows a strong resemblance. Both exhibit multiplet structure below the expected 4d excitation threshold and a broad, 10–20 eV wide peak above threshold followed by small peaks of decreasing intensity. AEAPS peaks are more intense and narrower than SXAPS peaks. The data are used to gain an understanding of the decay mechanism following the excitation of the core levels in these spectroscopies. The spectra recorded from oxidized metals do not show any major changes in the spectral features except for the chemical shift of the threshold. The shifts for all metal oxides are less than 1.0 eV except for Sm which is 2.5 eV. The similarity of the metal and oxide spectra indicates that the APS spectra are dominated by atomic rather than band effects.