Energy loss function of samarium

We present a combined experimental and theoretical work to obtain the energy loss function (ELF) or the excitation spectrum of samarium in the energy loss range between 3 and 200 eV. At low loss energies, the plasmon excitation is clearly identified and the surface and bulk contributions are distinguished. For the precise analysis the frequency-dependent energy loss function and the related optical constants (n and k) of samarium were extracted from the measured reflection electron energy loss spectroscopy (REELS) spectra by the reverse Monte Carlo method. The ps- and f-sum rules with final ELF fulfils the nominal values with 0.2% and 2.5% accuracy, respectively. It was found that a bulk mode locates at 14.2 eV with the peak width ~6 eV and the corresponding broaden surface plasmon mode locates at energies of 5-11 eV.