some additional comments:

- it is a bit tricky to operate ionisation chambers at this low energies (low pressure)
- some Beamlines have issues with higher harmonics (high angles of mirrors to get low cut off energies)
- preparation of good sample is tricky 


best regards

Stefan Mangold

Am 14.09.2023 um 06:09 schrieb Mike Massey <mmassey@gmail.com>:

The other difficulty I have experienced with P EXAFS is that a lot of the second-shell backscatterers are fairly weak, so picking that signal out is pretty difficult.

I have some spectra of minerals and that's where I've wanted to start with P EXAFS (since the structures are well-constrained). But as has been mentioned, low-frequency oscillations and background subtraction have massive impacts on the P K-edge EXAFS function (tested this by taking spectra of the same sample during different runs and getting different EXAFS due to slightly different background).

I don't think it's necessarily impossible, I just personally put it in the not-right-now basket.





On Sep 14, 2023, at 07:42, Mike Massey <mmassey@gmail.com> wrote:


In my experience the main difficulties with EXAFS on P (phosphate) come from two factors (not signal to noise, it's not hard to get a nice smooth line, but):

1) You've got 4 O atoms, guaranteed, so any other signal will be small and on top of that very strong signal generated from the first-neighbor O

Unfortunately,

2) You have very limited data range, either due to instrumental limitations, or due to interference from sulfur

Don't get me wrong I still have some data sitting around and I'd love to try P EXAFS analysis on it just to try and grasp that brass ring but...It's not the easiest task ever.

If you want good data quality "scan longer" is always an option. Some might think it's crazy but I do think I have some P XAS data where I took 30 or 60 scans, maybe overnight or something. The scans are so short that repeats are easy.


Hope this commentary is helpful.



Mike




On Sep 14, 2023, at 07:04, Marcelo Eduardo Alves <mealves@gmail.com> wrote:



Hi there,

I begin by examining phosphorus adsorption by goethite, hematite, and gibbsite.

Why is it difficult, if not impossible, to obtain EXAFS spectra at the P-K edge that can be properly used, i.e., spectra with a high signal-to-noise ratio, especially for dilute samples?

Would it be possible to use arsenic as a phosphorus proxy to get conclusions from As K-edge EXAFS data that could be extended to P?

Thank you.


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