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 <alexeyboub...@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" <ske...@anl.gov> > Date: 8/23/23 16:11 (GMT+01:00) > To: XAFS Analysis using Ifeffit <ifeffit@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 (ske...@anl.gov) > > > > *From:* Ifeffit <ifeffit-boun...@millenia.cars.aps.anl.gov> *On Behalf Of > *Zi Qi Chen > *Sent:* Tuesday, August 22, 2023 9:53 AM > *To:* ifeffit@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 > > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit >
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