[Ifeffit] S02

Matt Newville newville at cars.uchicago.edu
Fri May 25 09:58:32 CDT 2018


On Fri, May 25, 2018 at 9:01 AM Julian Ehwald <jehwald at gmail.com> wrote:

> Dear Matt,
> Thank you for your superfast answer. I obtained new data from the people
> at the beamline today, and the set contains both Total electron Yield and
> Total fluorescence yield. As far as I understand, they both tell us
> something about the absorption. Which is usually used for analysis? If I
> process them with Athena I get considerable differences…

​Please use the mailing list.

Either or both of total electron yied and total fluorescence yield can be
used for XAFS.  That is, total emission of high-energy electrons and
emission of fluorescence X-rays are both proportional to the absorption
cross-section for an atom, at least to first approximation.  There are
complications in using these. For X-ray fluorescence the main complication
is "over absorption" which happens in materials in which the element of
interest is high concentration (effects can be noticeable at ~1% and are
usually significant-but-correctable up to ~10%, and are nearly impossible
to correct above ~50% concentration).  For electron yield, the main
complication is that the electron escape depth is shallow enough that the
measurement may be more sensitive to the surface than the bulk of the
sample.  That sort of depends on how you define "surface" (the electrons
escape from 10s to 100s of Angstroms), but can be seen as an advantage if
surface sensitivity is what you want.

For both, using the data as XAFS means using mu ~ EmissionIntensity / I0.
 That's very different from transmission data, which often trips people up
when importing the data into Athena:  DO NOT use the log( EmissionIntensity
/ I0), use EmissionIntensity/I0.

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