[Ifeffit] calculating particle size from coordination numbers

[Georges Siddiqi]

Hi All,

I'm trying to use EXAFS data I have of Cu nanoparticles dispersed on SiO2
and ZnO to calculate their particle size.

Searching the archives, i've come by these topics and papers, which have
helped immensely, but I'm still a little bit in the dark about the
specifics of the fits:
http://www.mail-archive.com/ifeffit@millenia.cars.aps.anl.gov/msg02994.html
http://www.mail-archive.com/ifeffit@millenia.cars.aps.anl.gov/msg03430.html

http://pubs.acs.org/doi/full/10.1021/jp012769j
http://pubs.rsc.org/en/Content/ArticleLanding/1999/CP/a904654b#!divAbstract

So these discussions and papers make it clear that CNs for the 2nd or 3rd
coordination shells will give a more accurate picture of the particle size
(and even shape).  Also, just comparing SO2s between a foil and the sample
isnt the most accurate.

My initial thought was to get a good fitting model on Cu foil, obtain
coordination numbers which are very close to 1, then apply that same
fitting model to the Cu nanoparticles (for the Cu-SiO2 species we have TEM
data I can again calibrate myself with)

However, my specific problem is getting reasonable coordination numbers for
the Cu foil.
- I can set the SO2 to 1 and get a very good fit for the data, but this is
not useful for the nanoparticles
- I can give all paths the same SO2 variable, and get a fitted value close
to 1, but this isnt useful for comparing first and second shell CNs, as the
ratio will always be the same.
- And finally, when I try to give each scattering shell its own independent
CN, I again get a good fit, but while the first shell SO2 is close to 1,
the 2nd shell value is closer to 1.5

I've been playing with which variables are the same between paths, etc, and
I can get more reasonable numbers, but the problem then becomes that I cant
easily justify my fitting model.

Attached is my Artemis file for Cu foil.

Any help or suggestions with how to proceed (specifically with how to group
variables) would be much appreciated.  I apologize in advance if i'm asking
about a topic that's been covered extensively.

thanks,
Georges Siddiqui
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