The role of auto-ionization transitions in the formation of the extended fine structure of high-energy secondary electron spectra

Extended fine structure (EFS) of secondary electron (SE) spectra has been detected beyond the high-energy (similar to 720 and similar to 840 eV) LVV Auger lines in iron and nickel. Two mechanisms of its formation are considered: 1) direct transitions of electrons to the final state p according to Fermi's "golden rule'' and 2) second-order processes of auto-ionization type, passing through excitation of a core electron to an intermediate state q of the continuum with subsequent filling of the hole formed during this process by a valence electron and transition of the electron from the intermediate state q to the final state p. Interference of the direct wave with the wave reflected from neighboring atoms generates the EFS both in the final (p) and in the intermediate (q) state with two different periods determined by the wave numbers p and q. Comparison of calculated extended fine structures with the experimentally observed ones leads to the conclusion that the structure is formed by second-order auto-ionization processes. (C) 1998 American Institute of Physics. [S1063-7834(98)00409-2].