Resonant and Nonresonant Auger Recombination

Abstract

In the simplest picture the Auger process, named after its discoverer the French physicist Pierre Auger, can be considered as a two-step process. In the initial stage of the normal Auger process the atom is singly ionized. In the high-energy limit of the photoionization process the atom first relaxes in its core hole state. In a practically distinct second step, the core hole is then filled by an outer electron and the excess energy is released by means of photon emission or by emission of a second electron which is called the Auger electron (Figure 1a). When the binding energies of the initial core hole states are in the soft x-ray region (r≤ 1 keV), the Auger process is a strongly dominating decay channel. There are commonly used symbols for the emitted Auger electrons which are based on x-ray energy notations and indicate the initial- and the two final-state core holes, e.g., K - L 1 L 2,3. Alternatively, the orbital notations for the vacancies are used, e.g., 1s -1 → 2s -12p -1. Auger transitions, where the initial-state hole is in the same main shell as one or both of the final-state holes, are called Coster-Kronig (CK) or super Coster-Kronig (SCK) transitions, respectiveiy. The energy of the outgoing Auger electron is given by the difference of the total energy of the initial state of the system (atom, molecule, solid state) with a hole in an inner subshell and the final state with two holes in the outer subshells, e.g., E(K - L 1 L 2,3) = E[(K)+] - E[(L 1 L 2,3)2+]. The Auger emission is very sensitive in testing the quantum theory of the structure of the emitting system. Theoretical background and calculation methods will be discussed in more detail below. For recent review papers the reader is referred to Refs.1—6.