P000027
Optical Properties of Lanthanide Elements, Sm and Tb, Derived with Reflection Electron Energy Loss Spectroscopy
*Xiaohui Zhou (Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, P.R. China)
Jiamin Gong (Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, P.R. China)
Li Zhen (Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, P.R. China)
Sulyok Attila (Institute for Technical Physics and Materials Science Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Budapest, Hungary)
Menyhard Miklos (Institute for Technical Physics and Materials Science Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Budapest, Hungary)
Tokesi Karoly (Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), P.O. Box 51, Debrecen, Hungary)
Da Bo (Research and Services Division of Materials Data and Integrated System, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan)
Ding Zejun (Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, P.R. China)
The frequency dependent energy loss function and the related optical constants, , for two rare earth metals, samarium (Sm) and terbium (Tb), were derived in a wide energy loss (i.e. photon energy) range of 0-180 eV from reflection electron energy loss spectroscopy (REELS) spectra. The experimental measured REELS spectra normalized with the elastic peak intensity were analyzed by removing surface excitation effect, elastic scattering effect and multiple effect with our latest reverse Monte Carlo (RMC) technique. The RMC method quantitatively describes the electron energy loss spectra based on a direct physical modelling of the electron transport in the surface region of a sample. Our modeling of electron inelastic scattering with a dielectric function formalism includes the bulk excitation and the depth dependent surface excitation; hence, it allows the removal of surface excitation from the spectra. The RMC method also combines the optimization of the energy loss function in a simulated annealing procedure for the trial simulation of REELS spectrum in order to fit with the measured spectrum. The accuracy of the subtracted energy loss function was verified by applying the Thomas-Ritchie-Kuhn and the perfect-screening sum rules. By analyzing the plasmon energy and critical energy of the interband transition, we have determined the peak near 2.5-3.0 eV is due to plasmon excitation rather than the previous interpretation in terms of interband transition. The obtained electron inelastic mean free paths are found to be close to theoretical predications.