[Ifeffit] Estimation of Pt and Au particle size

[Barton, David (DG)]

Scott:

Thank you for your detailed and prompt response.  I look forward to testing out your example file of fitting Pt particle size, it should be a good starting point to begin this type of "rough" analysis.  After working though this "rough" analysis we will then consider if our data quality will allow for a more detailed analysis of particle shape or distribution.  Where we want to eventually take this analysis is to determine if we can measure differences in the particle size distribution in a series of samples.

Ifeffit Community:
I am still open to additional example Artemis files, especially if someone has a file that they would want to share related to fitting Gold particle sizes.

Regards,
Dave

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> Of Scott Calvin
> Sent: Tuesday, April 19, 2005 9:29 AM
> To: XAFS Analysis using Ifeffit
> Subject: Re: [Ifeffit] Estimation of Pt and Au particle size
> 
> 
> Hi David,
> 
> Sure thing. I'll send you a Pt file as a separate email; I'll also 
> send you a copy of the paper we're currently preparing for 
> publication. The final versions we used we're big Ifeffit scripts 
> rather than Artemis files, but I'm sure I can scare up a 
> representative Artemis file from earlier in the process.
> 
> Just a brief comparison of the two methods I've seen out there:
> 
> 1) Fit the coordination number of each shell. Anatoly Frenkel has 
> several publication related to this.
> 
> 2) Assume the crystallites are "roughly" spherical and constrain the 
> coordination numbers in a fit to reflect this. The only size-related 
> fitting parameter is then R, the radius of the crystallite. I have 
> written a few papers related to this method.
> 
> Method 1 has the advantage that it can in principle handle any 
> morphology; Anatoly has used it with supported catalysts (they may 
> even have been Pt, but I don't recall offhand) and distinguished 
> between shapes like rafts, hemispheres, etc..
> 
> Method 2 has the advantage that is uses only 1 size-related 
> parameter. For a complicated fit or one with limited data quality, 
> that's nice. On the other hand, if the morphology is far from 
> spherical (e.g. needles), then it doesn't work very well. This method 
> can even be used with an empirical standard (as opposed to a 
> theoretical standard like FEFF) to give a (rough) model-independent 
> estimate of size.
> 
> So I tend to think method 1 is better when you have a very uniform 
> sample, as can happen with supported catalysts, while method 2 is 
> often appropriate when you have a "messier" sample with roughly 
> spherical particles, as is often the case when wet chemical methods 
> are used.
> 
> It should also be noted thatusing both techniques there have been 
> many reports that for polydispersed samples EXAFS yields a mean 
> smaller than that found by other methods (e.g. Scherrer analysis). 
> Part of that can be explained by the different weightings inherent in 
> the different techniques (EXAFS reads a 10 nm and 10 micron 
> crystallite as essentially identical, but "notices" a 1 nm 
> crystallite, while XRD would find the 10 micron signal dominant), but 
> I am not yet convinced that there isn't something else at work as 
> well. My group is currently planning a follow-up study of Pt to 
> resolve this question.
> 
> --Scott Calvin
> Sarah Lawrence College
> 
> >Ifeffit Community:
> >
> >Over the past year or so I have seen several discussions of
> >estimation of metal cluster size (collections of several to hundreds 
> >of metal atoms) using coordination numbers derived from EXAFS 
> >fitting.  I was wondering if anyone on the list would be willing to 
> >share an example of their Artemis project file where this analysis 
> >was done successfully for Pt and/or Au particle sizes.  As a first 
> >pass I am just interested in roughly estimating an average particle 
> >size with future considerations for estimations of particle size 
> >distributions if data quality and theory allows.
> >
> >Thanks in advance to anyone willing to share their project files.
> >Given the number of experts in the field reading this list it just 
> >seemed to make sense to build upon the back giants.
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov 
> http://millenia.cars.aps.anl.gov/mailman/listi> nfo/ifeffit
>