Hi Melike,
If the 'before doping' system is a known material - i.e. a bulk standard
- I would fix N's, let R's, sig^2's, dEo, and So^2 be variables to fit.
While sig^2 may be similar between doped and undoped, I would not assume
that no disorder has been introduced on doping. I would consider
transferring So^2 from undoped standard to doped (assuming you are
fitting the same edge in both cases. You will have correlation between N
and sig^2 as well as between R and dEo.
dEo represents an offset correction to the Fermi level (model
calculation vs actual) but also corrects for where Eo is chosen when
extracting the EXAFS. A change in dEo could be due to a change in model
validity (i.e. model being used is less accurate for doped than for
standard undoped). Uncertainty in the fit value of dEo will likely be a
substantial fraction of dEo, so small changes may not be statistically
significant.
For comparing the two data sets, start with the visual...XANES, chi(k)
(maybe k^2*chi(k) or another k-weighting) and
the FT(k^2*chi(k)). That can help guide your interpretation of fit
results - if you see differences in low k but not high
k for example, or if your first shell looks broader but lower in
amplitude in the doped vs undoped potentially indicating some splitting
of nn distances (but then this may manifest as an increase in sig^2 if
you don't have data to high enough k to resolve a small splitting).
Rather generic advice...hope it helps...
cheers,
-R.
On 2022-03-10 4:04 a.m., Melike Babucci wrote:
Dear all,
For a reliable comparison of two EXAFS data sets (lets say before and
after Cu-doping), which parameters should be kept consant in the first
model?
I understand that sigma^2 values should be the same in two fittings,
and I would see a change in coordination numbers and deltaE0 and
deltar after Cu doping. Is that a good approach?
Does the new deltaE0 indicate a change in the conduction band energy?
Thanks in advance.
Best regards,
Melike
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