3.1.2.15 Lanthanides (4f) (rare-earth metals): Ce, Sm, Gd, Tb, Dy, Ho, Yb

This chapter discusses electronic structures of lanthanides (4f) (rare-earth metals): cerium (Ce), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), and ytterbium (Yb). The lanthanides are very reactive which makes it difficult both to observe a clean surface and to prepare single crystalline samples. There are two items which have been studied so far: SCLS and change in valency at the surface. Energy difference ΔH_II,III between divalent and trivalent rare-earth metals is shown. The bonding in Ce is found to be mainly metallic in character. Occupation numbers for α- and γ-Ce is tabulated. Charge density, surface and bulk, and photoemission (PE) spectra of α-Ce metals are figured out. Valence change at the surface of Sm metal is observed by probing the “free-electron density” via plasmon excitation in electron-energy-loss spectroscopy using primary energies 100···1000 eV. The two ion species A and B corresponding to the 4f⁵ and 4f⁶ states of Sm and the surface band structure of 15 Å Gd films on W(110) are shown. The (bulk) electron band structure of Tb metal has been determined at room temperature by means of angle-resolved photoemission experiments on Tb (0001). UP spectra of a Dy film demonstrating the increased contribution of the surface emission at 40 eV is illustrated. ARUPS experiments have been performed on Ho(0001) and the results compared to first- principles photocurrent calculations. ARUP spectra of the valence band and photoelectron spectra of the 4f levels of Yb metal with photon energies from 16.8··· 90 eV are shown.