Screening Effects in Core-Level Spectroscopies

Abstract

When a core hole is created in an atom the other electrons react to screen the hole. As a consequence of this sudden changes, in the number of core holes in a system lead to a number of final states in which the wave functions of the “spectator” electrons differ from the ground state. In this sense in all of the final states the hole is screened in some way. It is informative to consider the screening that occurs when a core electron is photoemitted. Here excitonic models often have remarkable success in describing the screening of the lowest lying level even in metallic solids. These models assume that there is a (partially) localized screening orbital which is unoccupied in the neutral ground state, but whose occupation in the final state lowers the energy of the system (see e.g. ref. 1). For adsorbates on metal surfaces the model is described by the insert of figure 1 where the screening orbitals are considered to lie above the Fermi level EF, in the initial state, but are pulled below Ef by the core hole.