Study of the inelastic mean free path in ytterbium nanofilms by Auger electron spectroscopy and X-ray photoelectron spectroscopy

Using Auger electron spectroscopy and X-ray photoelectron spectroscopy, we have measured the inelastic mean free path in ytterbium. This value is shown to be anomalously high in divalent metal films ($\sim$13–15 $\mathring{\mathrm{A}}$ at the energy of 92 eV). When ytterbium is transformed to the trivalent state, the inelastic mean free path becomes close to the typical values for most metals. This is due to the promotion of the $4f$-electron to the $5d$-level in the valence band and an increase in the excitation cross section for plasmon losses in Yb$^{3+}$ films.