Hi Mike, I would suggest that, as Carlo mentions, that because you cut off at 2200 eV, the post edge background function in purple might be skewed a bit. I might be use values ~2190 eV and 2164 eV? Though it appears to be a “flat” region where you place the points, it may actually not be all that flat if data was collected further out. Even if you were to collected new data, if this short range is used and the same approach to normalization is used, I don’t know if LCF would improve.
Chris > On Jan 15, 2019, at 8:23 PM, Mike Massey <mmas...@gmail.com> wrote: > > Hi Scott, > > > I collect up to 2240 eV often, because that's about where the mirror stops, > but end up truncating it at 2200 eV before fitting because sometimes I end up > with all sorts of non-systematic background things at higher energies, > depending on the sample. > > I still collect the data because it helps me to troubleshoot, but I chop it > before fitting because 2200 eV is the limit of what I normally consider > consistently "good data." I end up with spectra that, to my eye anyway, are > comparable. For dilute samples, I don't usually trust it beyond that. For > concentrated samples, I don't have a problem. > > > Thanks, > > > > Mike > > > >> On Jan 15, 2019, at 5:12 PM, Scott Calvin <dr.scott.cal...@gmail.com> wrote: >> >> Hi Mike, >> >> Is there a reason the data stops at 2200 eV—e.g., is there another edge just >> above that? >> >> —Scott >> >>> On Jan 15, 2019, at 8:02 PM, Mike Massey <mmas...@gmail.com> wrote: >>> >>> Thanks Riti and Carlo. >>> >>> Riti: will give it a go, thanks! I think the data are salvageable, it's >>> just a question of how... >>> >>> Carlo: Interesting point. In terms of how I'm fitting it, I just use the >>> LCF window to do a two-component fit. Nothing super fancy. >>> >>> But what you're suggesting is that maybe I have a misunderstanding in the >>> way I'm normalizing my data. That's entirely possible. I generally try to >>> get a nice flat background by following the "flat part" of the spectra but >>> in cases like this the pre- and post-edge lines end up not parallel. I can >>> force it to be parallel, and that helps the fit to behave better, but ends >>> up creating other normalization issues. >>> >>> >>> Much obliged for the responses so far. >>> >>> >>> >>> Mike >>> >>> >>> >>> >>>> On Jan 15, 2019, at 4:42 PM, Carlo Segre <se...@iit.edu> wrote: >>>> >>>> >>>> Hi Mike: >>>> >>>> How are you trying to fit it? It looks to me like the post edge line is >>>> not in the right place. You need to tune it by hand when you have such a >>>> short energy range after the edge since the normalization is critically >>>> dependent on how you set this line. >>>> >>>> carlo >>>> >>>>> On Tue, 15 Jan 2019, Mike Massey wrote: >>>>> >>>>> Hi All, >>>>> >>>>> >>>>> Does anyone have advice for LCF of spectra with a small edge step? >>>>> >>>>> I've recently found myself with more and more issues fitting spectra like >>>>> the one shown in the attached photo, where the spectrum is of good >>>>> quality, but the fits end up not working out due to normalization (as far >>>>> as I can tell). >>>>> >>>>> Sadly, I have so far ended up just throwing these fits out, but I'm >>>>> hoping there is a better solution out there that someone might be able to >>>>> recommend. >>>>> >>>>> One solution is "get more of the element of interest," as a beamline >>>>> scientist recently told me. I'm just reluctant to really load it up in >>>>> the data collection, because at 2 keV I get nervous about artifacts like >>>>> self-absorption. >>>>> >>>>> Is there a better way? What am I missing? >>>>> >>>>> Thanks for your thoughts, >>>>> >>>>> >>>>> >>>>> Mike >>>> >>>> -- >>>> 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 >>>> se...@iit.edu http://phys.iit.edu/~segre se...@debian.org >>>> _______________________________________________ >>>> 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 >>> >>> _______________________________________________ >>> 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 >> >> >> _______________________________________________ >> 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 > > _______________________________________________ > 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 _______________________________________________ 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
