Damn it... We should have placed bets to whose response is correct.. But it was a real black box, I should admit.
A.
________________________________________
From: ifeffit-bounces@millenia.cars.aps.anl.gov [ifeffit-bounces@millenia.cars.aps.anl.gov] on behalf of Dreher Marian [Marian.Dreher@psi.ch]
Sent: Wednesday, September 21, 2011 3:06 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] particle size and coordination number in Ru nanoparticles on carbon
Thanks everyone for your help, now everything is working fine. My Ru reference was simply way too thick which caused a lot of dampening in the signal.
From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Wayne W Lukens Jr
Sent: Dienstag, 20. September 2011 20:26
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] particle size and coordination number in Ru nanoparticles on carbon
Hi Marian,
There is a very nice paper by Scott Calvin that describes this in some detail:
J. Appl. Phys. 94:778–83 (2003)
Sincerely,
Wayne Lukens
On Tue, Sep 20, 2011 at 11:04 AM, Scott Calvin mailto:scalvin@sarahlawrence.edu> wrote:
Hi Marian,
My big tip is to look at the second nearest-neighbor CN as well, and even further out if you can get it. It's sometimes hard to pin down the near-neighbor coordination number because of issues like the one you describe. But the ratio of higher CNs to near-neighbor CN is quite diagnostic of small nanoparticles. (Actually, for reasons too lengthy to get in to at the moment, this method does tend to produce results a bit biased to the small side, so it's best to try the identical fitting model on a bulk standard for comparison.)
--Scott Calvin
Sarah Lawrence College
On Sep 20, 2011, at 1:50 PM, Dreher Marian wrote:
Dear Ifeffit Community,
I am currently trying to extract the particle size of Ru supported on carbon from EXAFS data. I also recorded spectra of a Ru foil as a bulk reference sample.
So, my approach is to fit the first coordination shell of my bulk reference, setting CN to 12. From that I get a value for s02. I'm then using this value in the first shell fit for the Ru nanoparticles in order to get the coordination number.
However, the fit suggests that CN is still pretty much 12. What is changing drastically, though, is sigma^2 which usually doubles in value compared to the bulk sample. That makes sense, I guess, since there might be higher disorder in the nanoparticles.
Obviously, there is a chance that my nanoparticles are rather big, in which case CN would be close to 12. However, STEM and HRTEM pictures suggest that the Ru particles are between 1 and 2 nm in diameter.
I'm just starting to get into EXAFS analysis and pretty clueless right now about how to approach this.
Happy about any input,
many thanks,
Marian.
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