HI Haifeng,
Suppose you measure Fe foil three times, and all three scans overlap.
They are aligned.
But suppose the edge positions are at 7116 eV instead of 7112 eV. The
calibration is off.
You can adjust to it, but, as Carlo mentioned, it is really an angle
correction, not simply a
shift in energy. It is better to have an accurate calibration to begin
with, then aligned and
calibrated would be the same.
Note: Choice of target calibration can differ - some use the X-ray data
booklet values
http://xdb.lbl.gov/
and some use the Kraft et al. values
https://aip.scitation.org/doi/abs/10.1063/1.1146657
Just state which calibration you are using when presenting/publishing.
-R.
On 2018-07-27 10:32 AM, Haifeng Li wrote:
Hi, Robert,
Thanks for your help.
One more question. What is the real difference between calibration and
alignment? Do they have specific meaning?
Thanks,
Haifeng
On Sun, Jul 22, 2018 at 5:45 PM, Robert Gordon <ragor...@alumni.sfu.ca
<mailto:ragor...@alumni.sfu.ca>> wrote:
Hi Haifeng,
Here's my take on what you described:
Two sample to be studied at the same edge using the same
reference. Three scans on A and three on
B are done with simultaneous reference.
First: compare the three reference scans for A. If they agree,
then compare the data scans. If they also look
similar (i.e. no evidence of changing in the beam), you can merge
the three data scans
on A right away. If the references don't agree, then you determine
by how much they differ (how much a correction
would be needed to bring them into alignment) and apply that same
correction to the data before merging.
It is not meaningful to merge data that is not aligned. (If the
sample scans show changes from scans 1 to 3,
then you need to rethink how to do the measurements)
Repeat for B.
Now compare the merged (corrected beforehand if necessary)
references for A and B. If they agree,
you can compare data for A and B (merged) directly. If they do
not, determine how much one reference
differs from the other and apply that same correction to, say, B,
that brings its reference into alignment with
A's reference, and then compare A and B
You align the references between samples to the same value in
order to do a meaningful comparison
between them. If you report energy positions of features in your
near-edge spectra, the reader
would need to know to what energy those positions are referenced.
When possible, I recommend references that have tabulated edge
values (i.e. metal foils). A reference
need not be the same edge as the one being studied. For arsenic,
as an example, the gold L3-edge is
quite close to the As K-edge and serves as a good reference. If
not possible to use a metal foil, use a
reference that another interested researcher could readily obtain
or has used. This allows for
comparison of reproducibility. If your reference looks nothing
like literature, you may have a problem
with the beamline or in how you processed the data. This should be
one of the first things you
check when you start taking data at the beamlne.
You should also note how the beamline was calibrated when you did
the measurements.
regards,
Robert
On 2018-07-22 1:21 PM, Haifeng Li wrote:
Dear ALL,
I am a beginner in Athena. Recently I got the spectra and I am
confusing about the data calibration and alignment. The manual
shows that calibrate the reference data of one scan and align
other reference data to that calibrated one.
Here I want to show examples. I have two samples A and B, Each
sample has three scans with the corresponding reference data. For
sample A, 1st scan is calibrated and the other two scans are
aligned to 1st scan. Then merge them into merged A. The same
procedures for sample B and get merged B. If I want to compare
XANES of sample A and B, do I need to align the merged reference
data between A and B? If so, why? My understanding is that all
scans (original data and merged data) in sample A and B are
calibrated to standard edge energy. Why do they need to align?
I appreciate your help.
Thanks,
Haifeng
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