A solution energy term (E_imp ) must be considered to explain the surface core-level shift (SCS) of photoemission spectroscopy (PES) (δ(PES)) for the occupied core-level of a Z-atom metal and the SCS of inverse photoemission spectroscopy (IPES) (δ(IPES)) for the unoccupied core-level of a (Z+1)-atom metal. In addition, the Coulomb interaction of surface atoms (U ^S_ff ) of Eu metal must be different from that of bulk atoms (U ^B_ff ) of Eu metal to explain consistently the δ(PES) of Eu metal and the δ(IPES) of Gd metal.

Keywords: Photoelectron spectroscopy, Surface core-level shift

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