Auger and photoelectron contributions to the electron-yield surface extended x-ray-absorption fine-structure signal
Résumé
The various electronic excitation channels which contribute to the production of photoelectrons and Auger electrons following x-ray absorption in a solid are discussed. In particular, we outline the contributions of elastic and inelastic photoelectrons and Auger electrons for the different electron-yield detection modes which are commonly used to record the (surface) extended x-ray-absorption fine structure [(S)EXAFS] of a sample. We demonstrate by theoretical considerations that the (S)EXAFS signals measured by different electron-yield detection modes exhibit identical phases and thus will yield identical neighbor distances. The amplitudes derived from the spectra, however, may be quite different since the inelastic and secondary photoelectron channel which contributes for some detection modes does not contain extended x-ray-absorption fine-structure (EXAFS) information. It is pointed out that amplitude transferability between data recorded in different modes can still be approximately preserved by suitable background subtraction procedures. Experimental total electron yield and elastic Auger-electron yield EXAFS spectra of Al metal are presented which confirm our theoretical considerations.