On Thursday, August 18, 2011 11:02:13 am Pieter-Jan Sabbe wrote:
I am trying to do a linear combination fit with Athena. To do that i want to first prepare my standard spectra. My unknown sample is (I presume) a combination of Cu and Cu(I)O (cuprite) and Cu(II)O (tenorite). I started with calibrating the Cu to 8979 eV as how the Athena manual say how to do it (I use the zero crossing point at the second derivative). This provided me an E0 and Eshift. I am doubting now for what I should do next: Cuprite and Tenorite have different oxidation states, meanin that the binding energies of the inner electrons will shift and in that way shifting the absorption edge of the compound. Should I look somewhere in a database (does that exist, or articles) for the absorption edge of cuprite and tenorite and set it like that or should I use the same E0 as i did for Cu?
Hi Pieter-Jan, If you are doing LCF in energy, two important things are: 1) That all your data be on the same energy grid. This means that either you perform your experiment on a very stable and reproducible monochromator or that you always measure a reference spectrum and use that to align all your data. 2) That your data all be normalized in a consistent, defensible, and reproducible manner. Weird normalization will introduce systematic errors into your data that might be quite large (as we saw in Monday's discussion on this topic -- you *did* read that discussion, didn't you?).
Another important thing for me, I have found some old data with some standard reference (powder spectra) measured in fluorescence mode, but my guess they are from different beamtimes, can I use data from different beamtimes/beamlines as standards in a linear combination fit?
Same caveat as above -- you need to be able to put all your data on the same energy grid. Another caveat is that a different beamline might have a different energy resolution or some other issue that adds an additional systematic uncertainty into your analysis. As long as you are mindful of that and as long as you deal correctly with the alignment issue, there is no reason that you cannot use standards measured elsewhere or elsewhen. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter