[Ifeffit] Re. Larch Energy Calibration

[Schoepfer, Valerie]

Hi Chris and Adam,

I'm actually looking at Mo, so the energy range is from about 19800 through 20200 eV on a Si(220) monochromator.  (But thank you for your Fe offer!)
The standards seem to be all from the Canadian Light Source, but going as far back as 2013...
I'm not looking to make the LCF perfect at this point, but it does seem like the deeper I go, the less confident I am that I have the correct standards. 

I'm doing alright in Athena with respect to the process, its just that I can't get Larch to align properly. I'll probably just use Athena for data prep, Larch just seemed nice to learn.  
But then in Athena I run into trouble with incorrect standards. One thing after another, you know?

Thanks-
Valerie

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Today's Topics:

   1. Re: Larch energy calibration (Matt Newville)


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Message: 1
Date: Wed, 3 Mar 2021 18:38:24 -0600
From: Matt Newville <newville at cars.uchicago.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Larch energy calibration
Message-ID:
        <CA+7ESbrGYtdjidL4X+rCUEi+DfmL3dUyG-R2R-FHffeqshSGTQ at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi Valerie,

On Tue, Mar 2, 2021 at 10:48 AM Schoepfer, Valerie < valerie.schoepfer at usask.ca> wrote:

> Hi,
>
>
>
> I am using Larch XAS Viewer for the first time to analyze some Mo 
> XANES data. It is fairly straightforward, however I am running into 
> problems with energy calibration, which leads to problems with Linear 
> Combination Fitting.
>
>
>
> Right now, which is likely wrong, I?m calibrating the energy of a 
> standard to the theoretical edge, then auto-aligning the samples to the standard.
> But how do reference foils fit in here? Reference foils don?t seem to 
> be tied to the sample like they are in Athena. Should I be manually aligning?
>
>
>
> Is there a general guidance or work flow?
>

It's possible that I do not fully understand the question or that this answer will veer a bit off the topic of your question.

For sure, energies need to be aligned properly for any multi-spectra comparison or linear method to work well. But it should be that you will have groups of spectra that all share a consistent energy calibration, say from the same beamline/beamtime.

If you do have a reference channel for every measurement, you can compare those reference channels.  Ideally, these will not vary for every
measurement - that would indicate a serious problem.   So, I think you
should be able to group spectra together as uniformly calibrated (hopefully all data from a day or more of beamtime at a particular beamline) and then make sure that the different groups of spectra.  Does that seem reasonable?

I have to admit that at my beamline I don't often have the luxury or need to run a reference foil for every scan, so we calibrate consistently ahead
of time.  I'm sure that leads to a bias in the software.   I guess I forgot
that Athena had the ability to read and tie a second spectrum as a "reference" and use that to auto-apply calibration.

Is it generally necessary to calibrate many spectra individually, or do people find that doing them in a few large groups is sufficient?

--Matt
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