HI!
You are new to XAFS? Welcome to the community. Many of the synchrotron
facilities host
courses annually on how to collect and analyze data. It can be very
helpful to participate in one
of these. There are also resources (tutorials) online that can help you
gain a better understanding
of the technique...e.g. https://urldefense.us/v3/__https://xrayabsorption.org/__;!!G_uCfscf7eWS!bCIzv24VWAWimBnVXbXJ29qP-BMF8p2K8KQ23BsuQPoQgPcPR_8vvPCDV2GS-ApKWSwpqi263HGbnKY6X7LH-6oBW-IsSuD3N-s3VxY$
With regards to your particular problem, LARCH's choice of E0 is not
unreasonable. What matters
most is that you are consistent in how you process your data. The E0
value is somewhat arbitrary
as it is intended to represent the onset of absorption, but structure in
the edge can complicate that.
When fitting, there is a parameter used (deltaE0) to correct for
discrepancies between the choice of
E0 and the calculated Fermi level.
A further idea to consider is how low in photo-electron momentum is
usable in EXAFS. For your data,
and in general, data going down an edge is not well-fit to a background
and is not going to be used
(and heavily suppressed by k-weighting when fitting). You don't have to
take the spline to k=0 (i.e. to E0).
For your data, I would probably stop at around 9020 eV and not use below
9040 when transforming
and fitting.
Check the literature on how others have handled similar compounds.
Again, what matters most is that
your choices for processing be reasonable and consistent.
cheers,
-R.
On 2024-05-13 7:08 p.m., Jan-Benedikt Weiss wrote:
Dear all, since I am new to XAFS analysis, I do not have a proper
understanding of how to chose E0 the right way if taking the first
maximum of the derivative of µ(E) is not an option. In my dataset
(K-edge of a Cu(I) coordination polymer with
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Dear all,
since I am new to XAFS analysis, I do not have a proper understanding of
how to chose E0 the right way if taking the first maximum of the
derivative of µ(E) is not an option. In my dataset (K-edge of a Cu(I)
coordination polymer with linear coordination environment), a huge
pre-peak far up the edge is present. Larch automatically detects E0 to
be in front of that peak which leads to a complicated subtraction of the
background in the EXAFS analysis (the spline does not align with the
shape of the edge; see attached plot) and will probably lead to other
problems. I thought of two alternative option to determine E0 but I do
not know if they are adequate.
Option 1: Take the second maximum of the derivative of µ(E) which
appears after the pre-peak (see attached plot). I guess this value is
still flawed by the pre-peak and therefore not accurate.
Option 2: Fitting a baseline curve under the pre-peak and select E0 as
the maximum of the derivative of that curve. Since this value will
probably lay underneath the pre-peak, it will not be suitable as the E0
value used in the background subtraction in the EXAFS analysis.
So do you have any suggestion on how to handle this case?
Best wishes
Jan
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