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 4f ⁸ final state components are found to be shifted to higher binding energy by 0.60±0.05 eV. Their larger linewidth as compared to the bulk lines indicates the presence of lowcoordinated sites at the low-temperature surface. The 4f-surface shift for trivalent DySb and DyTe is found to be only 0.2 eV and 0.4eV, respectively, as a consequence 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. Finally, a careful oxidation study of the cold-condensed Dy-films reveals that no manybody satellite has to be invoked to explain the appearance of a 6 eV peak in the spectra.