[Ifeffit] Peaks in Background Subtraction in Athena

Carlo Segre segre at iit.edu
Mon Mar 18 14:09:08 CDT 2019

Hi Nathan:

The peaks you see are pretty typical when you start at E0 and have the 
edge jump and a significant white line and it attempted to be "fit" to a 
smooth backgorund.  Since your FT window starts at least at k=2A, all of 
these wild oscillations are not a factor.  The important thing is that 
your FT is reasonable and that when you plot the weighted Chi(k) it looks 
relatively decent.

In short, you are usually OK with the default parameters


On Mon, 18 Mar 2019, Nathan Nakamura wrote:

> Hello,
> I am working on some data processing of ZrO2 thin films collected in
> fluorescence mode, and had a question regarding the background subtraction
> in Athena. When I use the default values, I see a large negative spike in
> the background curve (shown in BGsubtract1.png). I can vary the spline
> clamps and other parameters to reduce this (BGsubtract1.copy), but it does
> not seem to have any significant effect on the final EXAFS
> (EXAFScompare.png).
> My question is, do large spikes/instabilities on the edge like this need to
> be accounted for, or are they ok as long as the background fit after the
> edge seems fine? My thought is that as long as the EXAFS is not
> significantly affected, it should be fine, but I do not have a good sense
> for how the presence of this peak may impact the background curve beyond
> the absorption edge. I have also attached the project file in Athena for
> reference.
> Thanks,
> -Nathan

Carlo U. Segre -- Duchossois Leadership Professor of Physics
Interim Chair, Department of Chemistry
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org

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