Alright thanks to all of you. I already knew that there is a big relationship between the Fourier transform k-range and spectral resolution, but we couldn't get more energy range in the lab and wanted to see if EXAFS analysis was trustworthy this way or not.
A last question then: in the project I'm attaching 1_data.prj (other data, where I know I don't have enough energy range, but I wanted to try it), I get a FT plot with two well resolved peaks at around the bond lengths of the graphite sample (1.42Å in the same layer and 3.35Å between layers). Then as there is not enough k-range, we cannot extract any conclusions on that? (I guess we can but without much confidence, because then with another background removal, 2_data.prj, we obtain something different). Sorry for all the emails but it seemed so confusing to me..
Thank you again a lot,
Irina.
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From: Ifeffit
Thank you for the quick answer. Which range should I have for the EXAFS analysis to be meaningful? Like 200eV above the edge?
I am always uncomfortable when newcomers ask for "rules". Having a rule without understanding when and why it might apply seems counter-productive. Firstly, lets discuss the relation ship between "energy above the edge" and photoelectron wave number. The conversion constant between energy and wavenumber is k = sqrt( ETOK * (E-E0) ) where ETOK is the appropriate combination of fundamental constants (2m_e / hbar^2, where m_e is the mass of the electron and hbar is Planck's constant) about equal to 1 / 3.81. So, 10 inverse Angstroms is about 381 volts above the edge. The extent of the signal in k determines how well you can interpret an EXAFS signal in a quantitative sense. See this page in the Athena manual: http://bruceravel.github.io/demeter/documents/Athena/plot/krange.html Scott Calvin discusses this in his book. There is more information about EXAFS data reduction among the tutorials at http://xafs.org/Tutorials. As Fred and Robert have said, you need "enough" data range to make a useful interpretation of the EXAFS. 200 eV is not a lot -- that will leave you with only a small handful of independent measurements in your data, possibly not even enough to reliably determine a first shell bond length. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 743, Room 114 Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/ _______________________________________________ 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