Hi Mahmoud,

On Tue, Apr 18, 2017 at 5:11 AM, Al Humaidi, Mahmoud <mahmoud.alhumaidi@student.uni-siegen.de> wrote:
Hi , 

I want to ask please what is the shortest k-range one can use for "Forward Fourier transform" 

in my projects I used:

Spline range k 0.0 - 9.0
k range in Forward Fourier transform 1.0 - 9.0 A^-1

That should be OK, though it will limit the resolution and number of parameters you can use to model the data. 

Starting at k=1 Ang^-1 is often considered to be a bit too low for EXAFS analysis, as this is generally still in the XANES region where multiple scattering contributions dominate and where the background subtraction is more uncertain.   That is, starting a k=2 or 3 Ang^-1 might be a better choice.

  

I am trying to reduce the contribution of noise in FT .. 


Well, limiting the k-range does not always reduce the noise in the part of the signal you care about (R= 1 to 6 Ang).  It can, but just because k^2*chi(k) looks noisier at high k does not necessarily mean the data is only noisy in that range.  Mostly the noisiness at high-k implies that the signal-to-noise ratio is reduced, but that's at least partially because the signal goes down and may not mean the noise is going up.  OTOH, the measurements sometimes do get noisier at higher energy.....
 
the attached project shows nice fit ,,,but high phase shift toward lower R value ,, 
any recommendation please I will appreciate .. 
and thank you in advance , 


I don't understand why your "9%" merge data gets weird when making the spline go past 10 Ang^-1, but the "3%" ad "5%" merge data looks sort of OK to me going out to 11 or 12 Ang^-1.   I am not sure the signal is real.... If these are merged data, I'd suggest looking at the scan to scan variations to decide if the data is real.

Hope that helps,

--Matt




best regards 
Mahmoud AL Humaidi
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Mahmoud Al Humaidi     


Department of Physics, University of Siegen 
Emmy-Noether-Campus 
Walter-Flex-Str. 3, 57072 Siegen

Room : B-015
Tel :  +49 (0)  271 740 3727 
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