Background-free Auger line shape of Ag N 2,3VV measured with positron annihilation induced Auger electron spectroscopy

Abstract

Auger spectra for the Ag(100) N 2,3VV transition obtained utilizing positron annihilation induced Auger electron spectroscopy (PAES) are presented. This low energy transition of Ag is difficult to separate from the large secondary background which is present using electron induced Auger electron spectroscopy (EAES) and has not been studied extensively. In our measurements, the secondary electron background is eliminated by utilizing a positron beam whose energy is below the energy range of the of the Auger electrons. Measurements of the temperature dependence of PAES intensity, I PAES, and positronium fraction, f Ps, indicate that I PAES is proportional to the quantity (1 − f Ps. Electron energy spectra taken at high temperature ( f Ps ≈ 1) clearly demonstrate that the prominent low energy tail (LET) present in the PAES spectra is associated with Auger transitions and is not due to secondary electrons induced by collisions with the primary positron beam. The Auger line shape of the N 2,3VV transition of Ag(100) is accounted for in terms of the convolution of the density of states of the N 2,3 core levels and the density of states of the correlated two-hole final states estimated from the N 2,3 XPS core level spectra and the Auger line shape of the M 4VV transition. In addition, possible mechanisms leading to the production of the LET including a N 2N 3V transition followed by a N 3V-VVV transition and/or electron energy loss during the escape from the topmost layer are discussed.