Calculation of surface core-level shifts inSm1−xYxS

Abstract

We present a simple microscopic theory for the surface core-level shift in mixed-valence systems. In the case of a not fully screened final state, the core-level shift consists of an electronic and a Madelung-energy contribution. The electronic contribution is determined by the assumption of a rectangular $d$-band density of states. The Madelung-energy contribution is calculated with the use of reasonable assumptions for the screening of the ionic interactions. Using this theory we obtain results for the surface-energy shifts of the $4f$ state in ${\mathrm{Sm}}_{1-x}{\mathrm{Y}}_x\mathrm{S}$ as a function of the Y concentration. The numerical results agree well with recent photoemission data.