[Ifeffit] Differences between fluorescence and transmission of thesame sample

[Frenkel, Anatoly]

What can be done in this case, is not to use either flourescence or transmission data, - because both are bad by the reasons Bruce explained - but use corrections, if you cannot change your experimental geometry (different concentration of the sample or different thickness or different reactor cell).
 
What we do in these cases, if we must keep original thick sample for fluorescence measurements, we make the same sample prepared for transmission on a tape or as a pellet, that gives proper thickness to be free of any leakage or thickness effects that reduce oscillation intensity or introduce noise due to poor statistics. Then we compare EXAFS oscillations plotted together for the two samples: one measured in fluorescence in the cell you want to use in your in situ experiment, and the other meausred in tranmission in ideal conditions.
The former will have reduced intensity. You can manually find scaling factor that is needed to match two intensities. Based on many early papers (e.g., Kim, Stern and Heald, Physical Review B, Thickness effect in EXAFS data or something like that), this scaling factor is approximately constant. Once you found it, then you can take all your in situ data in flourescence and later on, during data processing and analysis, correct all the EXAFS data by scaling them up with the same factor.
 
Don't change the sample geometry midway, and do not apply similar correction to recover XANES. Other strategies should be used for XANES corrections.
 
Anatoly
 

________________________________

From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of Andrew Campos
Sent: Wed 5/5/2010 11:24 AM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] Differences between fluorescence and transmission of thesame sample



Dr. Ravel,

Thanks so much for the link and the advice! I appreciate it greatly. I
will advise my lab mates as such and may have to only use the
fluorescence data if that is indeed the case.

I also included the file where the lower temperature is included and
you might come to the same conclusion. The samples that I ran were
pre-sieved, and the ones included in the .prj file aren't so that
should be pursued prior to running the experiment. If they crush the
particle and sieve the sample, I think that we can be more certain
that this is not the case. This was very helpful!

Andrew


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