[Ifeffit] Shift in Eo when fitting PtO2 and similar samples

[Otal Eugenio]

Dear Chen,
Did you compare the spectra of Pt with the reference available here:
https://www.aps.anl.gov/files/APS-Uploads/DET/Detector-Pool/Beamline-Components/EXAFS_Filters/Reference_XRay_Spectra.pdf
Some edges, like Pd, are tricky.
Best, euG


(^ㅇᆽㅇ^)(=˃ᆺ˂=)(=🝦 ༝ 🝦=)




On Thu, Aug 24, 2023 at 5:02 AM alexeyboubnov <alexeyboubnov at gmail.com>
wrote:

> Dear Yanny, dear Shelly,
>
> I also came across this issue, with Pt and Ir L3 XAS. For these spectra,
> deltaE0 is systematically 10-12 eV, compared to K edge XAS spectra, where
> it is typically +/- a few eV.
>
> My explanation is as follows; if I am wrong or there are other
> explanations in the community, I would like to know:
>
> In the K edge case you define the actual edge step as your edge position
> E0 in Athena, which matches pretty well with the "E0" point that Artemis
> takes as k=0Å-1 when calculating the paths in FEFF. The difference deltaE0
> between what Artemis defines and what you define in Athena is thus small.
> Note that the pre edge peak (transition to bound states, 1s to 3d is weak)
> is left on the low energy side and typically ignored when choosing E0,
> because it is usually significantly smaller than the edge step.
>
> For L3 XAS, the white line is your transition to bound states, 2p to 3d,
> and is very intensive compared to the edge step. The actual edge step is
> then buried about 10 eV higher than where the white line onset is found. So
> when you define E0 as the white line onset, you "underestimate" the actual
> edge position by about 10 eV or higher. Artemis then corrects it and
> everything matches. If you define E0 at the white line peak as Shelly
> suggested, or maybe even after the white line, you will definitely be
> closer to theory, but that will also affect the background subtraction.
>
> Hopefully this is helpful!
>
> Cheers,
> Alexey
>
>
> -------- Original message --------
> From: "Kelly, Shelly Diane" <skelly at anl.gov>
> Date: 8/23/23 16:11 (GMT+01:00)
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Shift in Eo when fitting PtO2 and similar samples
>
> Hello Yanny:
>
>
>
> I’ve modeled a few Pt EXAFS spectra and have found that using an E0 at the
> top of the white line usually does a better job of getting the data close
> to the theory. This seems to be often the case with the L3-edges as they
> are rather broad compared to the K-edges of transition metals.  If you
> would like to share your project files with me. I can take a look.  14 eV
> seems to be too much and maybe an indication that there is a different type
> of atom in the first shell.
>
>
>
> B.T.W. Using the first derivative is great for XANES analysis, but often
> not the best choice for EXAFS.
>
>
>
> Kind regards,
>
> Shelly Kelly (skelly at anl.gov)
>
>
>
> *From:* Ifeffit <ifeffit-bounces at millenia.cars.aps.anl.gov> *On Behalf Of
> *Zi Qi Chen
> *Sent:* Tuesday, August 22, 2023 9:53 AM
> *To:* ifeffit at millenia.cars.aps.anl.gov
> *Subject:* [Ifeffit] Shift in Eo when fitting PtO2 and similar samples
>
>
>
> Dear all,
>
>
>
> I am looking at EXAFS of PtO2 powders and Pt particles supported on TiO2.
> I used a beta-PtO2 crystal structure data for the PtO2 EXAFS and after
> the first shell fit, I observed a large shift in Eo (delta Eo of ~14 eV) in
> my fit parameters. When I tried to fit the Pt foil to obtain the So2, the
> energy shift also seemed high (delta Eo of ~7 eV). I am wondering if there
> could be a problem in the selection of Eo prior to EXAFS analysis? I left
> the Eo as the energy at the first peak of first derivative (ifeffit
> default).
>
> All of the data were also aligned using the reference foil in Athena
> before looking at EXAFS. I am wondering what would have caused this shift?
> Any help is appreciated, thank you.
>
>
>
> Best regards,
>
> Yanny
>
>
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