[Ifeffit] particle size effects on XAFS spectra

Dominik Samuelis d.samuelis at fkf.mpg.de
Mon Jun 7 08:21:14 CDT 2010

Dear Rana,

yes, it will have effects on your XAFS spectra, but not really 
destructive. EXAFS only really vanishes if you have isolated atoms. As 
long as your particles still have several hundred atoms with some 
coordination shell-like ordering, EXAFS oscillations will show up.

However, the amplitude of the XAFS signals will be smaller than in bulk 
material, due to the lower average coordination number of the central 
atoms. If you e.g. have 5 nm particles (some 2000 atoms), already almost 
half of the atoms (~800) is sitting on the particle surface and 
therefore has a reduced coordination number.

There's a wealth of information in literature where people actually use 
this effect for determining the particle size from XAFS.

Another thing to keep in mind is that often it's not really clear how 
the surfaces of a particle looks like chemically - there might be 
adsorbates, or even passivation layers. If you're e.g. doing EXAFS on 
untreated 5nm Si particles, you can't really expect to see anything 
close to bulk Si, because the top layer might be SiO2

Best regards,

On 07.06.2010 14:49, Jatinkumar Rana wrote:
> Dear Users,
> I am working with the EXAFS technique for the characterization of my
> powder sample. I must admit that i am very much new to the technique and
> its analysis. I have read many tutorials on preparing sample for XAFS
> measurement (both transmission and fluoroscence). However, i am dealing
> with the powder having particle size much more smaller than one
> absorption length.
> I would like to know will it create any destructive effect on my XAFS
> spectra ??
> Many thanks in advance...
> Warm wishes,
> Rana
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Dr. Dominik Samuelis
d.samuelis at fkf.mpg.de
Max-Planck-Institut für Festkörperforschung
Max Planck Institute for Solid State Research
Heisenbergstr. 1
70569 Stuttgart
Phone +49-711-689-1769
Fax   +49-711-689-1722
Web   http://www.fkf.mpg.de/maier/

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