SURFACE EFFECTS IN DY, DYSB AND DYTE OBSERVED BY PHOTOELECTRON-SPECTROSCOPY

Cold condensed (100 K) Dy-films, as well as DySb and DyTe were studied by photoelectron spectroscopy using HeII and HeII excitation sources . The spectra were analyzed using the relative intensities and energy splittings of the individual 4f-multiplets from intermediate coupling calculations for bulk and surface multiplet components. At the surface of Dy the 4f8 final state components are found to be shifted to highe r binding energy by 0.60 +/- 0.05 eV. Their larger linewidth as compar ed to the bulk lines indicates the presence of low-coordinated sites a t the low-temperature surface. The 4f-surface shift for trivalent DySb and DyTe is found to be only 0.2 eV and 0.4 eV, respectively, as a co nsequence of a chemical shift of 1.1 eV towards higher binding energy as compared to the pure metal. The Dy atoms at the surface of DyTe are found to be stabilized by only 0.2 eV in their trivalent state. Final ly, a careful oxidation study of the cold-condensed Dy-films reveals t hat no many-body satellite has to be invoked to explain the appearance of a 6 eV peak in the spectra.