[Ifeffit] Ifeffit Digest, Vol 147, Issue 20

[Raj kumar]

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, <ifeffit-request at millenia.cars.aps.anl.gov>
wrote:

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> Today's Topics:
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>    1. Re: Peak at short distance in FT - YbVO4 nanoparticles
>       (Bruce Ravel)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 29 May 2015 12:52:38 -0400
> From: Bruce Ravel <bravel at bnl.gov>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Peak at short distance in FT - YbVO4
>         nanoparticles
> Message-ID: <55689956.8040302 at 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 at 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
> ****************************************
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