[Ifeffit] Differences between fluorescence and transmission of the same sample

[Bruce Ravel]

Andrew,

I suspect that you are seeing what Grant refers to in his tutorials as
"leakage".  That is, your transmission data appears to my eye to be
what happens when you have a wide spread in sample thickness under the
beam, ranging from gaps to very thick particles.

If you go to

  http://gbxafs.iit.edu/training/tutorials.html
 
And follow the link to the "Sample preparation" presentation, the
effect of leakage is shown on slide 16.

On the following slide, Grant points out that this thickness effect
always reduces amplitudes.  That is the case above the edge for your
data.  And if you normalize data distorted in that way, you end up
with an artificially enhanced pre-edge peak, again as in your data.

My US$0.02,
B


On Wednesday 05 May 2010 09:55:16 am Andrew Campos wrote:
> Hi everyone,
> 
> My lab mates are running in-situ H2 reduction of Cobalt/SiO2 catalysts
> using the Co K-edge and are obtaining differences between the
> fluorescence and transmission signals. The in-situ cell does have
> quite a bit of sample thickness (2-3 mm approx) and I was wondering if
> the fluorescence signal only has a penetration depth of a few
> micrometers. If this is the case that would explain it where the side
> that is further away from the heating element is more oxidized than
> the rest of the sample.
> 
> Has anyone run into this problem before? We're using the basic
> furnace/cryostat unit (in-situ cell manufactured by the exafsco) and a
> 13 element fluorescence detector (germanium diode).
> 
> I appreciate any insight into the issue, I have attached a
> fluorescence and transmission spectrum collected at the same time
> where the transmission and fluorescence are in the .prj file.
> 
> Thanks so much!
> Andrew
> 

-- 

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
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