X-ray photoemission study of the outermost levels of the rare earth metals

Standard X-ray photoemission technique has been applied to the study of 4f and valence states of the complete lanthanide series. The energy range of 15 eV below the Fermi level is very rich in peaks and structures. Apart from the valence band which has a relatively weak intensity, all the features observed in the spectra are due to the different final states 4fsup(n-1) which can be formed by removing one electron from the initial state 4fsup(n). The relative intensities of the allowed final states in photoemission are given by the squared fractional parentage coefficients which have been calculated. The energy separation between the different states can be taken from ultraviolet absorption spectra and their position relative to the Fermi level compared to a recent calculation (Herbst et al.). This analysis explains very well the detailed 4f-structures observed in the spectra of all rare earth metals. On the other hand, the spectra obtained by standard techniques are not quite suitable to study valence states. This is mainly due to the X-ray satellites and to the Kαsub(1,2) line width. In order to eliminate these obstacles an X-ray monochromator has been developed for the Al-line. A total instrumental line width of 0.3 eV or better (determined from the sharpness of metal Fermi edges) has been achieved. (Auth.)