[Ifeffit] LCF E0

[Bruce Ravel]

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 at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

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