Re: [Ifeffit] Ifeffit Digest, Vol 207, Issue 10
Dear All,
there is another publication about high precision measurements of X-Ray Absorption Edges from the early 90ies from the same group:
Measurement of the Energy of X‐Ray Absorption Edges
J. Stümpel P. Becker St. Joksch R. Frahm G. Materlik
First published: 16 April 1991
https://doi.org/10.1002/pssa.2211240224
The trick is that the authors don't use the monochromator in order to determine the energy of the edge, but instead an analyzer-crystal on a rotary stage with an encoder. This analyzer-crystal can be rotated to two different angles, where it fulfills the Bragg condition. Instead of measuring an absolute angle, they measure a difference of two angles, which is twice the Bragg-angle. This is more precise. They also measure the temperature of the crystal, which is essential to determine the lattice constant and to calculate the correct energy.
More than 15 years ago, Syed Khalid used the values from the PTB-publications to calibrate the monochromator at X18b, and he used these values to determine the temperature of the monochromator crystal. All energies of the edges of the 3d-metals could be nicely reproduced, and the deviations from the PTB-values were rather small and not jumping by several eV as the Bearden-values from the yellow book. Unfortunately, the web-page got lost after NSLS was shut-down (at least, I cannot find it again). Syed tried to convince his users to use the PTB-values for calibration, but they all refused since they had used the old values for decades and did not want to switch. There might have been also users from UOP.
Those, who listen to Jerry Seidler's Global XAFS Journal Club might remember the lecture by Joe Fowler: The tabulated values for the energies of fluorescence lines are ancient, some were still measured with photographic paper, and it is not much different for absorption edges.
I agree with Matt that new values are required, and we should compare our results!
With best regards,
Wolfgang
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Sent: Wednesday, 6 May, 2020 05:32:08
Subject: Ifeffit Digest, Vol 207, Issue 10
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Today's Topics:
1. Re: Reported W L3-edge and L2-edge energy (Matt Newville)
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Message: 1
Date: Tue, 5 May 2020 22:31:27 -0500
From: Matt Newville
All:
We are wondering if others agree that the reported values for the W L3 and W L2 edges are *incorrect*. We recently noticed the following:
The ?Edge? ? defined by the inflection point of the absorption edge step
When using the Ir L3 edge (11215.0 eV) as a calibration, the W L3- and L2-edges are *10203.4 eV* and *11542.4 eV*, respectively.
When using the Pt L3 edge (11564.0 eV) as a calibration, the W L3- and L2-edges are *10203.3 eV* and *11542.4 eV*, respectively.
These observations are thus different than the reported values of *10207.0 eV* and *11544.0 eV* for the L3 and L2 edges, respectively.
Thanks in advance for the discussion and feedback.
Simon R Bare
*Distinguished Scientist*
*SSRL, MS69*
*SLAC National Accelerator Lab*
*2575 Sand Hill Road*
*Menlo Park CA 94025*
simon.bare@slac.stanford.edu
Ph: 650-926-2629
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-- --Matt Newville <newville at cars.uchicago.edu> 630-252-0431
participants (1)
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Caliebe, Wolfgang