Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Ritimukta Sarangi]

Hello everyone,
In my experience, it is best to stay away from sulfate which has a hugely
intense peak subject to self absorption. At SSRL, we advice users to choose
Sodium Thiosulfate with the low lying and sharp S-S sigma star peak at
2472.02 eV and Tetraphenyl phosphonium bromide at 2146.96 eV for Phosphorus
(see Scott's paper at: J. Synchrotron Rad. 
 (2018). *25* ,
529-536)
Thanks,
Riti

On Thu, May 7, 2020 at 3:19 PM Matthew Marcus  wrote:

> For elements like P and S, people often use the energies of peaks.
> These are more immune to noise, energy-resolution effects and
> overabsorption than inflection points are.  For instance, on ALS 10.3.2,
> I used the sulfate peak of gypsum set at 2482.74eV.  I forget where I
> got that number.  Going down to soft X-rays, a common convention for the
> carbon edge is to use a pair of sharp peaks in CO2 gas at 292.74 and
> 294.96eV.
> mam
>
> On 5/7/2020 3:09 PM, Mike Massey wrote:
> > Hi Matt,
> >
> >
> > Indeed, in my experience (which is limited to one beamline at one
> > synchrotron facility for P XAS), once it is calibrated, the energy
> > selection tends to be quite stable, so I think you're on-target there.
> >
> > The trouble I still run into, though, is comparability of data between
> > studies. The difficulty is magnified by the fact that people tend to
> > identify certain near-edge features by the energy range at which they
> > occur. I do the same, of course, but I also try to carefully document
> > the material and energy I used to calibrate the monochromator.
> >
> > For the P K-edge, it doesn't really seem like people have settled on a
> > convention for calibrating the monochromator, unlike in the case of
> > iron, for example (where one just uses a foil and sets some feature of
> > that spectrum to their preferred value). If everyone was using the same
> > thing all would be happy, but most people use different materials and
> > different values. So datasets for P at the K-edge really aren't too
> > comparable just yet.
> >
> > Sorry to hijack the conversation, it's just an issue I've been mulling
> > over for a few years. The discussion of energy calibration values made
> > me think of it again.
> >
> >
> > Best,
> >
> >
> >
> > Mike
> >
> >
> >
> >
> >> On May 8, 2020, at 8:51 AM, Matt Newville 
> >> wrote:
> >>
> >> 
> >> Hi Mike,
> >>
> >>
> >> On Tue, May 5, 2020 at 10:56 PM Mike Massey  >> > wrote:
> >>
> >> On a tangentially related topic, I find that phosphorus K-edge XAS
> >> energy calibration conventions are still in a bit of a "Wild West"
> >> state, with a wide variety of materials and values in use for
> >> energy calibration. As an extreme example, one or two frequently
> >> cited papers in my field from the 2000s don't even report the
> >> material or value used for energy calibration, and only show
> >> portions of the spectra on an energy axis with values relative to
> >> an unknown E0.
> >>
> >>
> >> I have never measured a P K edge, or indeed any edge lower in energy
> >> than the S K edge (ignoring some X-ray raman work).  But if one is
> >> using a Si(111) double-crystal monochromator where P or S is
> >> approximately the low-energy (high-angle) limit, then it really should
> >> be that the calibration does not drift much and cannot be too wrong at
> >> low energies.
> >>
> >> That is, a mono calibration is controlled by a d-spacing and angular
> >> offset. Normally (or perhaps, in my experience), "re-calibrating" is
> >> done by changing the angular offset, leaving the d-spacing alone.
> >> That is, the d-spacing is presumably known, at least to within some
> >> thermal drift.
> >> If that is the case that the d-spacing really is not changing and what
> >> needs to be refined is the angular offset, then setting the offset at
> >> relatively high energy edges will be much more sensitive, and changing
> >> the angular offset to that a high-energy edge is correct should move
> >> lower energy edges by a smaller amount.   The corollary is that you
> >> have to move the offset a lot to move the P  K edge around, and that
> >> would have a larger (and ever-increasing) impact on higher energy
> >> edges such as Ca, Fe, Cu or Mo.
> >>
> >> The counter-argument is also true:  d-spacing has a bigger effect on
> >> the high-angle / low-energy edges.
> >>
> >> So, if you believe the mono d-spacing (or you believe the beamline
> >> scientist who believes it ;)) then calibrate at the highest energy you
> >> can.   The Kraft values don't go very low in energy.
> >>
> >> All that said, if using a different mono crystal such as InSb or more
> >> exotic crystals, I have no idea how stable those are.
> >>
> >>
> >> I too have picked my own material and value, and will be the first
> >> to acknowledge that I did so out of necessity and ease of
> >> comparison to other available data, 

Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Matt Newville]

Hi Mike, Matthew,


On Thu, May 7, 2020 at 5:55 PM Mike Massey  wrote:

> I agree Matthew, I also tend to use the primary K-edge peak for P
> calibration, but one issue to be wary of is attenuation/flattening of the
> primary peak (if one is using a concentrated sample).
>
> Gypsum sounds like a good material to use for S, since it is commonly
> available and probably not too variable. My material of choice for P
> (lazulite) might fail on both counts, so it might be a poor choice.
>
>
>
We're always on the lookout for better sulfur standards.  We find scotch
tape (magic tape that is), actually has pretty reproducible XANES and is
easy to come by.  Double-sided tape seems slightly different.

We tend to find gypsum slightly unreliable as a sulfur standard as there is
some variation in samples. Attached is a plot of 6 different gypsum samples
we've run (all in fluorescence), from a variety of user groups over a few
years.   You can see that there are differences in the low energy peaks and
large variations in the main sulfate peak intensity.  But the energy
position is stable.  Some of the variations may be due to over-absorption,
but the low-energy peaks suggest that "gypsum" is sometimes not high purity.

As I alluded to earlier, we never calibrate the energy at S, we just
measure it. We regularly check Fe and Cu.  These rarely vary by more than
0.5 eV unless we have "calibrated" to a
user-preferred-but-we-know-to-be-incorrect value, and we believe we have
the lattice constant pretty good to reproduce the Kraft values.   The
gypsum peak positions are pretty reliable and are definitely well below
2482 eV, more like 2481.75 eV.

For sure, we would be very interested in trying a Bond spectrometer like
Stumpfel et al user (or the clever Bond-like approach that Pettifer and
Hermes used before them).  We don't have a lot of room in our station for a
large diffractometer, but we do have access to area detectors these days,
so it is possible that multiple simultaneous reflections from fine Si
powder could be used.

--Matt
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Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Trudy Bolin]

Hello, all. It's been a long time since I've been in touch. Yes, energy
calibration is always an issue.  Its especially important for lower-Z XAFS.

I feel that edge and transition energies should be recorded, but depending
on the beamline and facility the absolute calibrations are hard to
establish.  So, its hard to say what the absolute value should be...?  I'm
curious to know more about the discussion about the W L-edges.

On Thu, May 7, 2020 at 5:55 PM Mike Massey  wrote:

> I agree Matthew, I also tend to use the primary K-edge peak for P
> calibration, but one issue to be wary of is attenuation/flattening of the
> primary peak (if one is using a concentrated sample).
>
> Gypsum sounds like a good material to use for S, since it is commonly
> available and probably not too variable. My material of choice for P
> (lazulite) might fail on both counts, so it might be a poor choice.
>
>
>
> Mike
>
>
>
>
>
> > On May 8, 2020, at 10:19 AM, Matthew Marcus  wrote:
> >
> > For elements like P and S, people often use the energies of peaks.
> These are more immune to noise, energy-resolution effects and
> overabsorption than inflection points are.  For instance, on ALS 10.3.2, I
> used the sulfate peak of gypsum set at 2482.74eV.  I forget where I got
> that number.  Going down to soft X-rays, a common convention for the carbon
> edge is to use a pair of sharp peaks in CO2 gas at 292.74 and 294.96eV.
> >mam
> >
> >> On 5/7/2020 3:09 PM, Mike Massey wrote:
> >> Hi Matt,
> >> Indeed, in my experience (which is limited to one beamline at one
> synchrotron facility for P XAS), once it is calibrated, the energy
> selection tends to be quite stable, so I think you're on-target there.
> >> The trouble I still run into, though, is comparability of data between
> studies. The difficulty is magnified by the fact that people tend to
> identify certain near-edge features by the energy range at which they
> occur. I do the same, of course, but I also try to carefully document the
> material and energy I used to calibrate the monochromator.
> >> For the P K-edge, it doesn't really seem like people have settled on a
> convention for calibrating the monochromator, unlike in the case of iron,
> for example (where one just uses a foil and sets some feature of that
> spectrum to their preferred value). If everyone was using the same thing
> all would be happy, but most people use different materials and different
> values. So datasets for P at the K-edge really aren't too comparable just
> yet.
> >> Sorry to hijack the conversation, it's just an issue I've been mulling
> over for a few years. The discussion of energy calibration values made me
> think of it again.
> >> Best,
> >> Mike
>  On May 8, 2020, at 8:51 AM, Matt Newville 
> wrote:
> >>>
> >>> 
> >>> Hi Mike,
> >>>
> >>>
>  On Tue, May 5, 2020 at 10:56 PM Mike Massey  > wrote:
> >>>
> >>>On a tangentially related topic, I find that phosphorus K-edge XAS
> >>>energy calibration conventions are still in a bit of a "Wild West"
> >>>state, with a wide variety of materials and values in use for
> >>>energy calibration. As an extreme example, one or two frequently
> >>>cited papers in my field from the 2000s don't even report the
> >>>material or value used for energy calibration, and only show
> >>>portions of the spectra on an energy axis with values relative to
> >>>an unknown E0.
> >>>
> >>>
> >>> I have never measured a P K edge, or indeed any edge lower in energy
> than the S K edge (ignoring some X-ray raman work).  But if one is using a
> Si(111) double-crystal monochromator where P or S is approximately the
> low-energy (high-angle) limit, then it really should be that the
> calibration does not drift much and cannot be too wrong at low energies.
> >>>
> >>> That is, a mono calibration is controlled by a d-spacing and angular
> offset. Normally (or perhaps, in my experience), "re-calibrating" is done
> by changing the angular offset, leaving the d-spacing alone.  That is, the
> d-spacing is presumably known, at least to within some thermal drift.
> >>> If that is the case that the d-spacing really is not changing and what
> needs to be refined is the angular offset, then setting the offset at
> relatively high energy edges will be much more sensitive, and changing the
> angular offset to that a high-energy edge is correct should move lower
> energy edges by a smaller amount.   The corollary is that you have to move
> the offset a lot to move the P  K edge around, and that would have a larger
> (and ever-increasing) impact on higher energy edges such as Ca, Fe, Cu or
> Mo.
> >>>
> >>> The counter-argument is also true:  d-spacing has a bigger effect on
> the high-angle / low-energy edges.
> >>>
> >>> So, if you believe the mono d-spacing (or you believe the beamline
> scientist who believes it ;)) then calibrate at the highest energy you
> can.   The Kraft values don't go very low in energy.
> >>>
> 

Re: [Ifeffit] Ifeffit Digest, Vol 207, Issue 14

[Christopher Chantler]

Dear all

This is an excellent thread. Just to give some background literature, you will 
be aware of the calibration of X-ray energies by diffraction (either like Kraft 
or better accuracy from the NIST group and Dick Deslattes, etc). This remains 
the best method for beamline calibration, though the mono is usually affected 
by heatload and detuning to shift the energies. [So you want either a 4-bounce 
or an analyser 'mono'].

You will also be aware of the International Tables of Crystallography Volume C 
Section 4.2.2 [Not our XAFS one, Volume I, but the main Physical Tables 
Volume]. The old issue summarised a lot of details about current known and 
not-known accuracy of X-ray energies and is embedded in the NIST website, 
though the original publication[s] Deslattes et al. are in many ways superior. 
However, Volume C is coming out with a new edition [soon*] and the summary of 
the known and unknown accuracies and what to do about them is in the new 
section 4.2.2. It should be available this year, I understand.

Secondly, by far the best edge energy determinations are those of Kraft et al., 
and these were based around the subset of transition metals and K edges. Most 
other edges have not been published with an absolute energy measurement, so 
they really do flop around in the literature. This is a major and important 
[urgent] task that maybe we can all help with. The issue of stability of lines, 
crystals etc. is a closely related and important issue.

The issue is compounded at lower energies and for L edges. One of the best 
current examples is that of the recent Mendenhall et al. publication on 
copper...

I hope this thread has emphasised the importance of this work and that we would 
all like more progress in this area

Very best wishes
Chris

--
Christopher Chantler, Professor, FAIP, Fellow American Physical Society
Editor-in-Chief, Radiation Physics and Chemistry
Chair, International IUCr Commission on XAFS; CIT, CCN
IPP, International Radiation Physics Society
School of Physics, University of Melbourne
Parkville Victoria 3010 Australia
+61-3-83445437 FAX +61-3-93474783
chant...@unimelb.edu.au
 
chant...@me.com
http://optics.ph.unimelb.edu.au/~chantler/xrayopt/xrayopt.html
http://optics.ph.unimelb.edu.au/~chantler/home.html



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Subject: Ifeffit Digest, Vol 207, Issue 14

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Today's Topics:

   1. Re: Reported W L3-edge and L2-edge energy (Matthew Marcus)
   2. Re: Reported W L3-edge and L2-edge energy (Mike Massey)


--

Message: 1
Date: Thu, 7 May 2020 15:17:20 -0700
From: Matthew Marcus 
To: ifeffit@millenia.cars.aps.anl.gov
Subject: Re: [Ifeffit] Reported W L3-edge and L2-edge energy
Message-ID: 
Content-Type: text/plain; charset=utf-8; format=flowed

For elements like P and S, people often use the energies of peaks.
These are more immune to noise, energy-resolution effects and
overabsorption than inflection points are.  For instance, on ALS 10.3.2,
I used the sulfate peak of gypsum set at 2482.74eV.  I forget where I
got that number.  Going down to soft X-rays, a common convention for the
carbon edge is to use a pair of sharp peaks in CO2 gas at 292.74 and
294.96eV.
mam

On 5/7/2020 3:09 PM, Mike Massey wrote:
> Hi Matt,
>
>
> Indeed, in my experience (which is limited to one beamline at one
> synchrotron facility for P XAS), once it is calibrated, the energy
> selection tends to be quite stable, so I think you're on-target there.
>
> The trouble I still run into, 

Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Mike Massey]

I agree Matthew, I also tend to use the primary K-edge peak for P calibration, 
but one issue to be wary of is attenuation/flattening of the primary peak (if 
one is using a concentrated sample).

Gypsum sounds like a good material to use for S, since it is commonly available 
and probably not too variable. My material of choice for P (lazulite) might 
fail on both counts, so it might be a poor choice.



Mike





> On May 8, 2020, at 10:19 AM, Matthew Marcus  wrote:
> 
> For elements like P and S, people often use the energies of peaks. These are 
> more immune to noise, energy-resolution effects and overabsorption than 
> inflection points are.  For instance, on ALS 10.3.2, I used the sulfate peak 
> of gypsum set at 2482.74eV.  I forget where I got that number.  Going down to 
> soft X-rays, a common convention for the carbon edge is to use a pair of 
> sharp peaks in CO2 gas at 292.74 and 294.96eV.
>mam
> 
>> On 5/7/2020 3:09 PM, Mike Massey wrote:
>> Hi Matt,
>> Indeed, in my experience (which is limited to one beamline at one 
>> synchrotron facility for P XAS), once it is calibrated, the energy selection 
>> tends to be quite stable, so I think you're on-target there.
>> The trouble I still run into, though, is comparability of data between 
>> studies. The difficulty is magnified by the fact that people tend to 
>> identify certain near-edge features by the energy range at which they occur. 
>> I do the same, of course, but I also try to carefully document the material 
>> and energy I used to calibrate the monochromator.
>> For the P K-edge, it doesn't really seem like people have settled on a 
>> convention for calibrating the monochromator, unlike in the case of iron, 
>> for example (where one just uses a foil and sets some feature of that 
>> spectrum to their preferred value). If everyone was using the same thing all 
>> would be happy, but most people use different materials and different 
>> values. So datasets for P at the K-edge really aren't too comparable just 
>> yet.
>> Sorry to hijack the conversation, it's just an issue I've been mulling over 
>> for a few years. The discussion of energy calibration values made me think 
>> of it again.
>> Best,
>> Mike
 On May 8, 2020, at 8:51 AM, Matt Newville  
 wrote:
>>> 
>>> 
>>> Hi Mike,
>>> 
>>> 
 On Tue, May 5, 2020 at 10:56 PM Mike Massey >>> > wrote:
>>> 
>>>On a tangentially related topic, I find that phosphorus K-edge XAS
>>>energy calibration conventions are still in a bit of a "Wild West"
>>>state, with a wide variety of materials and values in use for
>>>energy calibration. As an extreme example, one or two frequently
>>>cited papers in my field from the 2000s don't even report the
>>>material or value used for energy calibration, and only show
>>>portions of the spectra on an energy axis with values relative to
>>>an unknown E0.
>>> 
>>> 
>>> I have never measured a P K edge, or indeed any edge lower in energy than 
>>> the S K edge (ignoring some X-ray raman work).  But if one is using a 
>>> Si(111) double-crystal monochromator where P or S is approximately the 
>>> low-energy (high-angle) limit, then it really should be that the 
>>> calibration does not drift much and cannot be too wrong at low energies.
>>> 
>>> That is, a mono calibration is controlled by a d-spacing and angular 
>>> offset. Normally (or perhaps, in my experience), "re-calibrating" is done 
>>> by changing the angular offset, leaving the d-spacing alone.  That is, the 
>>> d-spacing is presumably known, at least to within some thermal drift.
>>> If that is the case that the d-spacing really is not changing and what 
>>> needs to be refined is the angular offset, then setting the offset at 
>>> relatively high energy edges will be much more sensitive, and changing the 
>>> angular offset to that a high-energy edge is correct should move lower 
>>> energy edges by a smaller amount.   The corollary is that you have to move 
>>> the offset a lot to move the P  K edge around, and that would have a larger 
>>> (and ever-increasing) impact on higher energy edges such as Ca, Fe, Cu or 
>>> Mo.
>>> 
>>> The counter-argument is also true:  d-spacing has a bigger effect on the 
>>> high-angle / low-energy edges.
>>> 
>>> So, if you believe the mono d-spacing (or you believe the beamline 
>>> scientist who believes it ;)) then calibrate at the highest energy you can. 
>>>   The Kraft values don't go very low in energy.
>>> 
>>> All that said, if using a different mono crystal such as InSb or more 
>>> exotic crystals, I have no idea how stable those are.
>>> 
>>> 
>>>I too have picked my own material and value, and will be the first
>>>to acknowledge that I did so out of necessity and ease of
>>>comparison to other available data, rather than because I thought
>>>it was correct.
>>> 
>>>The issue of calibration conventions and values definitely seems
>>>to be one that 

Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Matthew Marcus]

For elements like P and S, people often use the energies of peaks. 
These are more immune to noise, energy-resolution effects and 
overabsorption than inflection points are.  For instance, on ALS 10.3.2, 
I used the sulfate peak of gypsum set at 2482.74eV.  I forget where I 
got that number.  Going down to soft X-rays, a common convention for the 
carbon edge is to use a pair of sharp peaks in CO2 gas at 292.74 and 
294.96eV.

mam

On 5/7/2020 3:09 PM, Mike Massey wrote:

Hi Matt,


Indeed, in my experience (which is limited to one beamline at one 
synchrotron facility for P XAS), once it is calibrated, the energy 
selection tends to be quite stable, so I think you're on-target there.


The trouble I still run into, though, is comparability of data between 
studies. The difficulty is magnified by the fact that people tend to 
identify certain near-edge features by the energy range at which they 
occur. I do the same, of course, but I also try to carefully document 
the material and energy I used to calibrate the monochromator.


For the P K-edge, it doesn't really seem like people have settled on a 
convention for calibrating the monochromator, unlike in the case of 
iron, for example (where one just uses a foil and sets some feature of 
that spectrum to their preferred value). If everyone was using the same 
thing all would be happy, but most people use different materials and 
different values. So datasets for P at the K-edge really aren't too 
comparable just yet.


Sorry to hijack the conversation, it's just an issue I've been mulling 
over for a few years. The discussion of energy calibration values made 
me think of it again.



Best,



Mike




On May 8, 2020, at 8:51 AM, Matt Newville  
wrote:



Hi Mike,


On Tue, May 5, 2020 at 10:56 PM Mike Massey > wrote:


On a tangentially related topic, I find that phosphorus K-edge XAS
energy calibration conventions are still in a bit of a "Wild West"
state, with a wide variety of materials and values in use for
energy calibration. As an extreme example, one or two frequently
cited papers in my field from the 2000s don't even report the
material or value used for energy calibration, and only show
portions of the spectra on an energy axis with values relative to
an unknown E0.


I have never measured a P K edge, or indeed any edge lower in energy 
than the S K edge (ignoring some X-ray raman work).  But if one is 
using a Si(111) double-crystal monochromator where P or S is 
approximately the low-energy (high-angle) limit, then it really should 
be that the calibration does not drift much and cannot be too wrong at 
low energies.


That is, a mono calibration is controlled by a d-spacing and angular 
offset. Normally (or perhaps, in my experience), "re-calibrating" is 
done by changing the angular offset, leaving the d-spacing alone.  
That is, the d-spacing is presumably known, at least to within some 
thermal drift.
If that is the case that the d-spacing really is not changing and what 
needs to be refined is the angular offset, then setting the offset at 
relatively high energy edges will be much more sensitive, and changing 
the angular offset to that a high-energy edge is correct should move 
lower energy edges by a smaller amount.   The corollary is that you 
have to move the offset a lot to move the P  K edge around, and that 
would have a larger (and ever-increasing) impact on higher energy 
edges such as Ca, Fe, Cu or Mo.


The counter-argument is also true:  d-spacing has a bigger effect on 
the high-angle / low-energy edges.


So, if you believe the mono d-spacing (or you believe the beamline 
scientist who believes it ;)) then calibrate at the highest energy you 
can.   The Kraft values don't go very low in energy.


All that said, if using a different mono crystal such as InSb or more 
exotic crystals, I have no idea how stable those are.



I too have picked my own material and value, and will be the first
to acknowledge that I did so out of necessity and ease of
comparison to other available data, rather than because I thought
it was correct.

The issue of calibration conventions and values definitely seems
to be one that merits continued discussion. It has been
interesting to watch things evolve over time in the case of iron,
for example (it's good to know that 7110.75 is a candidate
calibration value...) I appreciate Matt's detailed thoughts, and
the data that he's been working with. Thanks Matt!


Cheers,



Mike






On May 6, 2020, at 3:32 PM, Matt Newville
mailto:newvi...@cars.uchicago.edu>>
wrote:


Hi Simon,

This is definitely a timely discussion for me, as I've been
spending part of the quartine working on collating data and
expanding datasets for an XAFS spectral database.  I'm hoping to
have something ready for public comment and to start asking for
contributions of data in a 

Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Mike Massey]

Hi Matt,


Indeed, in my experience (which is limited to one beamline at one synchrotron 
facility for P XAS), once it is calibrated, the energy selection tends to be 
quite stable, so I think you're on-target there.

The trouble I still run into, though, is comparability of data between studies. 
The difficulty is magnified by the fact that people tend to identify certain 
near-edge features by the energy range at which they occur. I do the same, of 
course, but I also try to carefully document the material and energy I used to 
calibrate the monochromator.

For the P K-edge, it doesn't really seem like people have settled on a 
convention for calibrating the monochromator, unlike in the case of iron, for 
example (where one just uses a foil and sets some feature of that spectrum to 
their preferred value). If everyone was using the same thing all would be 
happy, but most people use different materials and different values. So 
datasets for P at the K-edge really aren't too comparable just yet.

Sorry to hijack the conversation, it's just an issue I've been mulling over for 
a few years. The discussion of energy calibration values made me think of it 
again.


Best,



Mike




> On May 8, 2020, at 8:51 AM, Matt Newville  wrote:
> 
> 
> Hi Mike, 
> 
> 
>> On Tue, May 5, 2020 at 10:56 PM Mike Massey  wrote:
>> On a tangentially related topic, I find that phosphorus K-edge XAS energy 
>> calibration conventions are still in a bit of a "Wild West" state, with a 
>> wide variety of materials and values in use for energy calibration. As an 
>> extreme example, one or two frequently cited papers in my field from the 
>> 2000s don't even report the material or value used for energy calibration, 
>> and only show portions of the spectra on an energy axis with values relative 
>> to an unknown E0.
>> 
> 
> I have never measured a P K edge, or indeed any edge lower in energy than the 
> S K edge (ignoring some X-ray raman work).  But if one is using a Si(111) 
> double-crystal monochromator where P or S is approximately the low-energy 
> (high-angle) limit, then it really should be that the calibration does not 
> drift much and cannot be too wrong at low energies.  
> 
> That is, a mono calibration is controlled by a d-spacing and angular offset. 
> Normally (or perhaps, in my experience), "re-calibrating" is done by changing 
> the angular offset, leaving the d-spacing alone.  That is, the d-spacing is 
> presumably known, at least to within some thermal drift. 
> If that is the case that the d-spacing really is not changing and what needs 
> to be refined is the angular offset, then setting the offset at relatively 
> high energy edges will be much more sensitive, and changing the angular 
> offset to that a high-energy edge is correct should move lower energy edges 
> by a smaller amount.   The corollary is that you have to move the offset a 
> lot to move the P  K edge around, and that would have a larger (and 
> ever-increasing) impact on higher energy edges such as Ca, Fe, Cu or Mo.  
> 
> The counter-argument is also true:  d-spacing has a bigger effect on the 
> high-angle / low-energy edges. 
> 
> So, if you believe the mono d-spacing (or you believe the beamline scientist 
> who believes it ;)) then calibrate at the highest energy you can.   The Kraft 
> values don't go very low in energy.  
> 
> All that said, if using a different mono crystal such as InSb or more exotic 
> crystals, I have no idea how stable those are.
> 
> 
>> I too have picked my own material and value, and will be the first to 
>> acknowledge that I did so out of necessity and ease of comparison to other 
>> available data, rather than because I thought it was correct.
>> 
>> The issue of calibration conventions and values definitely seems to be one 
>> that merits continued discussion. It has been interesting to watch things 
>> evolve over time in the case of iron, for example (it's good to know that 
>> 7110.75 is a candidate calibration value...) I appreciate Matt's detailed 
>> thoughts, and the data that he's been working with. Thanks Matt!
>> 
> 
>> Cheers,
>> 
>> 
>> 
>> Mike
>> 
>> 
>> 
>> 
>> 
 On May 6, 2020, at 3:32 PM, Matt Newville  
 wrote:
 
>>> 
>>> Hi Simon,
>>> 
>>> This is definitely a timely discussion for me, as I've been spending part 
>>> of the quartine working on collating data and expanding datasets for an 
>>> XAFS spectral database.  I'm hoping to have something ready for public 
>>> comment and to start asking for contributions of data in a few weeks, but 
>>> I'll be happy to have more discussion about that sooner too. 
>>> 
>>> I generally believe that the monochromator I use at GSECARS is both 
>>> well-calibrated and reasonably accurate.  That is, with 2 angular encoders 
>>> with a resolution of >130,000 lines per degree and an air-bearing, I 
>>> believe the angular accuracy and repeatability are very good.  I believe 
>>> there are equally good moons in existence.   As Matthew 

Re: [Ifeffit] Reported W L3-edge and L2-edge energy

[Matt Newville]

Hi Mike,


On Tue, May 5, 2020 at 10:56 PM Mike Massey  wrote:

> On a tangentially related topic, I find that phosphorus K-edge XAS energy
> calibration conventions are still in a bit of a "Wild West" state, with a
> wide variety of materials and values in use for energy calibration. As an
> extreme example, one or two frequently cited papers in my field from the
> 2000s don't even report the material or value used for energy calibration,
> and only show portions of the spectra on an energy axis with values
> relative to an unknown E0.
>
>
I have never measured a P K edge, or indeed any edge lower in energy than
the S K edge (ignoring some X-ray raman work).  But if one is using a
Si(111) double-crystal monochromator where P or S is approximately the
low-energy (high-angle) limit, then it really should be that the
calibration does not drift much and cannot be too wrong at low energies.

That is, a mono calibration is controlled by a d-spacing and angular
offset. Normally (or perhaps, in my experience), "re-calibrating" is done
by changing the angular offset, leaving the d-spacing alone.  That is, the
d-spacing is presumably known, at least to within some thermal drift.
If that is the case that the d-spacing really is not changing and what
needs to be refined is the angular offset, then setting the offset at
relatively high energy edges will be much more sensitive, and changing the
angular offset to that a high-energy edge is correct should move lower
energy edges by a smaller amount.   The corollary is that you have to move
the offset a lot to move the P  K edge around, and that would have a larger
(and ever-increasing) impact on higher energy edges such as Ca, Fe, Cu or
Mo.

The counter-argument is also true:  d-spacing has a bigger effect on the
high-angle / low-energy edges.

So, if you believe the mono d-spacing (or you believe the beamline
scientist who believes it ;)) then calibrate at the highest energy you
can.   The Kraft values don't go very low in energy.

All that said, if using a different mono crystal such as InSb or more
exotic crystals, I have no idea how stable those are.


I too have picked my own material and value, and will be the first to
> acknowledge that I did so out of necessity and ease of comparison to other
> available data, rather than because I thought it was correct.
>
> The issue of calibration conventions and values definitely seems to be one
> that merits continued discussion. It has been interesting to watch things
> evolve over time in the case of iron, for example (it's good to know that
> 7110.75 is a candidate calibration value...) I appreciate Matt's detailed
> thoughts, and the data that he's been working with. Thanks Matt!
>
>
Cheers,
>
>
>
> Mike
>
>
>
>
>
> On May 6, 2020, at 3:32 PM, Matt Newville 
> wrote:
>
> 
> Hi Simon,
>
> This is definitely a timely discussion for me, as I've been spending part
> of the quartine working on collating data and expanding datasets for an
> XAFS spectral database.  I'm hoping to have something ready for public
> comment and to start asking for contributions of data in a few weeks, but
> I'll be happy to have more discussion about that sooner too.
>
> I generally believe that the monochromator I use at GSECARS is both
> well-calibrated and reasonably accurate.  That is, with 2 angular encoders
> with a resolution of >130,000 lines per degree and an air-bearing, I
> believe the angular accuracy and repeatability are very good.  I believe
> there are equally good moons in existence.   As Matthew Marcus pointed to
> the Kraft paper (which used an older source but 4-bounce mono to improve
> resolution), we find that Fe foil is definitely better defined as 7110.75
> and Cu foil is between 8980.0 and 8980.5 eV.  That is, we've measured
> multiple foils, found their first derivatives, and refined the d-spacing
> and angular offset.  We do this about once per run, and the offsets tend to
> be very consistent.   For sure, there is some question about whether the
> Kraft numbers are perfect.   For sure, putting Fe foil at 7110.75 +/- 0.25
> eV appears to be "most right" to us.
>
> I also believe that we should probably re-measure these metal foils (and
> other compounds) with a single calibration set for both Si(111) and
> Si(311).  We will probably have time to do that this summer in the time
> between "beamline staff can get back to the beamline" and "open for outside
> users".
>
> What I can tell you now is:  I have some data on W metal, WO2, and WO3
> measured all at the same time on our bending magnet line, with Si(111).  An
> Athena project for this is attached (W.prj).   I cannot vouch for the
> absolute calibration.
>
> I also attach a set of foils (V, Fe, Cu, Mo) measured with the same
> calibration (and Si(111) on our ID line), after adjusting d-space and
> offset to be close to the Kraft values (CalibratedFoils2013.prj).
>
> I also attach a set of foils (Fe, Cu, Au L3, Au L2, Au L1, Pb L3, Pb L2,
> Pb L1 edges) measured in