Yup. In fact, self absorption, in the correct sense, can help reduce
"self-absorption" in the misnomer sense! That's how the grazing-exit method
works.
I might also note that although many elaborate schemes have been proposed for
correcting for the effect, they all require knowing things about the
sample that you don't always know, e.g. the exact geometry of something that
isn't planar, or the exact composition. I find that the simple parameterization
which comes from a thick-planar-sample model works reasonably well as an
empirical method with an unknown parameter. Still, I wouldn't necessarily trust
Debye-Waller (ss2) values taken from EXAFS on strongly overabsorbed samples,
even with a correction that gets the right coordination number.
mam
On 4/3/2016 7:04 PM, Matt Newville wrote:
Hi Matthew,
On Sun, Apr 3, 2016 at 8:13 PM, Matthew Marcus <mamar...@lbl.gov
<mailto:mamar...@lbl.gov>> wrote:
<Rant>
It shouldn't be called 'self-absorption'. That's a misnomer, which seems
to have come from a 1992
paper (Troger, et. al."Full correction of the self-absorption in
soft-fluorescence extended x-ray-absorption fine structure", PRB 46,3283 (1992).
The effect was described and analyzed in a 1982 paper, which called it an
"attenuation factor": Goulon, et. al. "On experimental attenuation factors of
the amplitude
of the EXAFS oscillations in absorption, reflectivity and luminescence
measurements", J. Physique 43, 539 (1982).
</Rant>
mam
Thanks!! I completely agree, though I wasn't aware of the historical precedence for the
mistake. Using "over-absorption" is a far better term.
In X-ray fluorescence, "self-absorption" actually means the attenuation of
fluorescence generated within a sample as it travels out of the sample. For
over-absorption in XAFS, the issue is measuring absorption in fluorescence mode when the
concentration of the absorbing element is not infinitesimal or when the sample thickness
is not infinitesimal.
--Matt
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