[Ifeffit] Au-foil (fcc) splitted peak

[mkarabiy]

2011/10/11, Kaiser, Julian <julian.kaiser at helmholtz-berlin.de>:
> Dear Wayne and Grant Bunker,
>
> thanks a lot for the explanation!
> To be honest, I didn't know the Ramsauer-Townsend effect before.
> I think it's ok to show the spektra without subtracting out the scattering
> phase. As long as I know what's going on and as long as I can explain it it
> will be fine.
>
> Thanks so much for your help!
> Julian
>
> ________________________________________
> Von: ifeffit-bounces at millenia.cars.aps.anl.gov
> [ifeffit-bounces at millenia.cars.aps.anl.gov]" im Auftrag von "grant
> bunker [bunker at iit.edu]
> Gesendet: Sonntag, 9. Oktober 2011 21:38
> Bis: ifeffit at millenia.cars.aps.anl.gov
> Betreff: [Ifeffit] Au-foil (fcc) splitted peak
>
> Julian - the scattering amplitudes of all elements have structure in them
> that are connected to electron scattering  (Ramsauer-Townsend) resonances
> within the backscattering atom.  For light elements (e.g. O, S, Fe) they
> occur at energies that are lower than the typical transform range, so they
> usually are ignored.  For heavier scatterers like Au there are strong minima
> and maxima in the Au scattering amplitude over the transform range. From a
> signal processing point of view, these amplitude modulations look like
> beats, which normally are due to different distances interfering.   In the
> case of Au back scatterers, even if there is only one physical distance, you
> will get multiple peaks (perhaps overlapping).   Mathematically the fourier
> transform is the distance distribution convoluted with the fourier transform
> of the amplitude.
>
> So, how do you deal with it?  First, if you know what's going on that may be
> enough.  Alternatively, if all the scatterers are the same, it's not
> difficult to divide out the scattering amplitude and subtract out the
> scattering phase before the transform to obtain an "optical transform",
> which eliminates the effect you're seeing. I don't know if that is supported
> by ifeffit but it's not hard to do.  This approach is less useful if you
> have multiple types of scatterers (e.g. Au, S) because if you do the
> compensation for one type of scatterer it screws it up for the others.
> Techniques like regularization are probably better in that case.
>
> hope that helps
>
> grant bunker
>
>
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