<title>Core Level Resonances In The Rare Earths Monitored By Electron Energy Loss Spectroscopy</title>

Abstract

Core electron excitations of rare earth metals have been studied by electron energy loss spectroscopy (EELS) in reflection geometry. Electron energy loss spectra of 3d and 4d excitations are investigated along the rare earth series, and are compared to X ray absorption and synchrotron partial yield spectra. In the study of inner-shell transitions the electron energy loss technique has an important advantage over photon absorption studies, in that electric dipole forbidden transitions may be induced. In 4d→4f excitations new transitions are clearly identified for the light rare earths, while the heavy rare earths show strong enhancement of already dipole allowed levels of high J as the primary energy is lowered. Even stronger non-dipole effects are observed in 3d→4f excitation spectra, although the range of multiplet energies is much less than for 4d→4f. Finally, it is shown that core level excitations in EELS can be successfully used in the surface chemistry of rare earths as a valence monitor during surface reactions.