Core-level binding-energy shifts during metal adsorption and compound formation: Yb/Ni(100)

A model for core-level shifts in metallic overlayers is introduced. The model is based on a decomposition of the shift into partial shifts which are related to specific structural aspects of the interface system. The model is applied to the Yb/Ni(100) overlayer system which has been studied by He ii and Al Kα excited photoelectron spectroscopy. The deposition of Yb is investigated at two substrate temperatures, room temperature and 670 K. At 670 K ordered low-energy electron diffraction structures are seen, and at higher Yb depositions intermixing with the substrate occurs. At room temperature no ordered structures are seen. The low mobility of the atoms furthermore prevents strong intermixing with the substrate. It is shown that an analysis of the divalent and trivalent Yb shifts provides detailed structural information about the Yb/Ni(100) overlayer system.