Research Activity
Auger electron spectroscopy in coincidence with threshold photoelectrons
Figure 1 shows a schematics of experimental apparatus used for threshold photoelectron-Auger
electron coincidence spectroscopy. We have two electron analyzers,
for Auger electrons and for threshold electrons. The resolution is
practically determined by the photon band width, not by that of Auger
analyzer, which is used just to separate the Auger final states.
We are interested in resonant enhancement of double photoionization
(DPI) process near an atomic inner shell threshold. In our case, DPI
leads to the creation of slow electrons whose emission dynamics is
not yet completely elucidated. At the inner shell thresholds, DPI
is described in a first approximation as the creation of a zero kinetic
energy photoelectron, which we call threshold photoelectron, and an
inner shell vacancy followed by Auger decay where a double charged
ion and an Auger electron are produced. Due to the post collision
interaction (PCI), the interaction between the photoelectron, the
Auger electron and the atomic field which changes during the Auger
decay, energy exchange between the escaping electrons occurs. Consequently,
threshold electrons can be observed, not only at threshold, but also
above the inner shell threshold. This phenomenon of PCI distortion
of threshold electron yield is well known and has been widely investigated
both theoretically and experimentally.However, a detailed understanding
of dynamics of slow electron production is still missing.
Figure 1. Experimental apparatus of threshold photoelectron-Auger electron coincidence spectroscopy
Figure 2 shows a threshold photoelectron-Auger electron coincidence spectrum
in the vicinity of the Ar2p threshold. In this two dimensional spectrum,
the coincidence signals are plotted as a function of the fast electron
energy and the photon energy. With the linear relation between the
fast electron energy and the photon energy, the final states appear
as diagonal lines on the two dimensional spectrum. In this electron
energy region, the Ar2+ final states have the electron configuration
of (3p4). We can recognize three different channels, corresponding
to the 3P, 1D and 1S states. Projecting the coincidence signals in
each channel onto the horizontal axis, we obtain the threshold electron
spectra for different doubly charged ionic final states.
Figure 2.
Auger electron spectrum in coincidence with a threshold photoelectron in the vicinity of the Ar2p ionization thresholds