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P. Joglekar, R. Gladen, V. Chirayath, A. Fairchild, S. Kalaskar, K. Shastry, Q. Dong, S. Hulbert, R. Bartynski, W.S.M. Werner, A. Weiss:
"Measurement of the full electron spectrum associated with the Ag N₃VV Auger transitions: Evidence for the contribution of multi-electron Auger processes";
Journal of Electron Spectroscopy and Related Phenomena, 235 (2019), 16 - 22.

We report the first measurement of the full energy spectrum (down to 0 eV) of electrons emitted from the surface
of Ag(100) as a result of the N3VV Auger transition. A comparison with a Monte-Carlo model was used to obtain
an estimate of the contribution of multi-electron Auger processes to the low energy part of the Auger spectrum.
The experimental Auger spectrum was obtained in time coincidence with photo-emitted 4p3/2 core electrons
from Ag using Auger-Photoelectron coincidence spectroscopy (APECS). The coincidence condition in APECS can
remove most, but not all, spectral contributions from events unrelated to the Auger transition. The remaining
contributions to the APECS spectrum from Auger-unrelated events, which are significant, were determined from
a series of coincidence measurements of inelastically scattered valence band photoelectrons. The contribution
from Auger-unrelated events was subtracted from the APECS Auger spectrum of Ag(100) to obtain the full Auger
spectrum down to 0 eV. The resulting spectrum includes, in addition to Auger electrons emitted without energy
loss, inelastically scattered Auger electrons. We observe that the spectral weight of the low energy tail (LET) in
the APECS spectrum is reduced by more than a factor of two after subtracting the Auger-unrelated contributions.
However, the intensity of the LET after this subtraction is still two times the integrated intensity in the Auger
peak. A Monte Carlo model that includes the inelastic transport of the N3VV Auger electrons through the surface
showed that LET produced by the inelastic scattering of the Auger electrons has the same intensity as the
integrated intensity in the Auger peak. The excess intensity in the experimental LET provides strong evidence
that the Auger related spectrum also includes contribution from multiple electron emissions that are intrinsic to
the creation and/or the Auger decay of the core hole. Our estimate shows that as low as 20% to as high as 60% of
the core hole decay events result in the emission of more than one Auger electron from Ag (100). This result
demonstrates the need for a better understanding of the contribution of valence-electron correlations to the
entire CVV Auger spectrum down to 0 eV.

Electron spectroscopy Coincidence spectroscopy Auger electron Photoelectron Background elimination Low energy tail (LET)