[Ifeffit] Double picks on Near Edge region.

Kelly, Shelly D. SKelly at anl.gov
Wed Sep 12 09:02:40 CDT 2007

SDK> Hi Pei-chang, See below for some ideas.

To whom it may concern,
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Dear Prof.; 
  Here have some questions about Zn doped LiNbO3 single crsystal 
EXAFS fitting problem, we did the similar EXAFS absorption spectra 
as you can see the attach reference paper Fig 7, that shows 
double picks on Near Edge region, and our questions are,
(1) Base on your great knowledge, how comes about these
    two picks, and is it normal?

SDK>  I'm not sure what you are asking.  It is common to find "decorations" in the region near the absorption edge of many elements. There are several different ways to think about the reason for the "decorations".  One way is to think about the density of states that are available for the promotion of the 1s electron (K-edge).  Another way to describe them is from long multiple scattering paths of the photoelectron.  Near the edge the photoelectron has very little kinetic energy.  This means that the mean-free path of the photoelectron (how far the photoelectron can travel without loosing coherence) is long, so that long multiple scattering paths can have a significant contribution.  See http://www.xafs.org/Tutorials?action=AttachFile&do=get&target=Newville_xas_fundamentals.pdf 
I think that you would benefit from reading this tutorial.

(2) On Artemis program R-figure display, we can find a great pick
    appeared in 0~1 angstrom range (k range=1~12), but we find
    this pick disappeared under (k range=2~12) parameter choosing
    ,so is it relation to question (1)?

SDK> This is not uncommon.  It is often difficult to remove the background properly from the low k-region of the EXAFS signal.  Often K-min values of 2 or 3 are used.

(3) If we want to cut near edge contribution, how should we deal with
    these double picks? choose the rear EXAFS spectrum (aviod these
    two picks)? Or using Athena background removal it?
SKD>  I'd use a k-range starting at 2.


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