Re: [Ifeffit] Ifeffit Digest, Vol 147, Issue 20

Hi Bruce, The comments are very helpful to assure my data processing and for future experiments. Yes, all measurements were obtained in Dispersive EXAFS mode. As for i know (at least until my preparation time) the bulk sample (first one) doesn't contain the Hf impurities. However, i will double check that point. Regards, Raj On Fri, May 29, 2015 at 7:00 PM, wrote:

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Today's Topics:

1. Re: Peak at short distance in FT - YbVO4 nanoparticles (Bruce Ravel)

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Message: 1 Date: Fri, 29 May 2015 12:52:38 -0400 From: Bruce Ravel To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Peak at short distance in FT - YbVO4 nanoparticles Message-ID: <55689956.8040302@bnl.gov> Content-Type: text/plain; charset=windows-1252; format=flowed

On 05/29/2015 11:54 AM, Raj kumar wrote:

...

Recently, i have performed EXAFS for YbVO4 bulk (prepared through sintering process) and nanoparticles (at room temperature). Nanoparticles were synthesized by co-precipitation technique and their EXAFS was measured by passing the prepared solution using peristaltic pump. After all subtraction (background and solvent), nanoparticles XAS data were recovered and processed for the fitting. After Fourier transform, it was observed that both nanoparticles posses an additional short peak (or shoulder) at about 1.2 A from bulk. Since the peak appears much closer to 1 A, i suspect this may due to artifact or bad background subtraction. Hence, i would like to know the way to eliminate this peak at short distance.

Hi Raj,

A few comments:

1. Your bulk sample (the first one in the list) may have a bit of Hf in it it. It's hard to tell, but the mu(E) seems to be trending upward right at the end of the data, which is the approximate edge energy of Hf L3. I got a slightly better background removal by changing the end of the spline range to 600. But this a minor detail. The real story seems to be that ....

2. You data are pretty noisy. If you plot chi(R) out to 10 Angstroms (which is, presumably, well beyond where you should expect to see good signal in your data), you get a sense of how the level of noise manifests itself in chi(R). To my eye, the peak/shoulder at about 1.2 that you are asking about is of about the same size as the level of noise in your data.

You are asking how to get rid of a feature in the data that is aesthetically unpleasing. I don't think that's the right question.

Your data are what they are. Your data are noisy and measured over a rather short energy range. That doesn't give you a lot of choices about how aesthetically appealing you can make the Fourier transform be.

You seem to be operating Athena correctly and there aren't any magic buttons that will make your short, noisy data longer or less noisy. I don't see anything obviously wrong in how you are processing your data and -- short of using PhotoShop ;) -- I don't see any defensible way of making the feature at 1.2 go away.

Am I correct in thinking that these data are measured in the dispersive geometry? If so, my suggestion is to reconsider how you make your samples. This kind of experiment is VERY sensitive to the homogeneity of the sample. You have to take extraordinary care to make your samples as homogeneous as possible. I suspect most of the glitchy little points in your data are indicative of sample inhomogeneity.

You also should worry about purity of your source material. Granted, it canbe very difficult to obtain rare earth metal samples that are elementally pure. But if your data range is short because of other edges, then you need samples that are more pure.

HTH, B

-- Bruce Ravel ------------------------------------ bravel@bnl.gov

National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 535A Upton NY, 11973

Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/

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End of Ifeffit Digest, Vol 147, Issue 20 ****************************************