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

Ritimukta Sarangi ritimukta at gmail.com
Fri May 8 00:06:12 CDT 2020


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. <http://journals.iucr.org/s>
 (2018). *25* <http://journals.iucr.org/s/contents/backissues.html>,
529-536)
Thanks,
Riti

On Thu, May 7, 2020 at 3:19 PM Matthew Marcus <mamarcus at lbl.gov> 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 <newville at cars.uchicago.edu>
> >> wrote:
> >>
> >> 
> >> Hi Mike,
> >>
> >>
> >> On Tue, May 5, 2020 at 10:56 PM Mike Massey <mmassey at gmail.com
> >> <mailto:mmassey at gmail.com>> 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
> >>>     <newville at cars.uchicago.edu <mailto:newville at 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 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 2016 (again, using Si(111) on our
> >>>     ID line), also with the same calibration values
> >>>     (FeCu_Au_Pb.prj).  I'm pretty certain these use the same
> >>>     d-spacing as the 2013 Foils to at least 5 digits.   For
> >>>     completeness, all of the raw data files are also under
> >>>
> https://github.com/XraySpectroscopy/XASDataLibrary/tree/master/data
> >>>
> >>>     In my experience, the Pb L3 edge value has the biggest variation
> >>>     in the literature, with values ranging from 13035 to 13055 eV
> >>>     (possibly a typo somewhere along the line).  Fortunately, the
> >>>     Kraft-based calibration splits the difference and puts the value
> >>>     at 13040 eV.
> >>>
> >>>     For W in particular, I will look if I have measured this recently
> >>>     on our ID line.  I can tell you that I use CdWO4 as a phosphor
> >>>     and use that to focus our X-ray beam.   I use this trick all the
> >>>     time: any tail from the beam penetrating the phosphor is shortest
> >>>     at the peak of the white-line and for CdWO4 that is always
> >>>     between 10210 and 10215 eV.
> >>>
> >>>     I hope that helps.  I am interested in trying to get all these
> >>>     values as accurately as possible, so any comments or suggestions
> >>>     would be most welcome.
> >>>
> >>>     --Matt
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>     On Tue, May 5, 2020 at 5:14 PM Bare, Simon R
> >>>     <srbare at slac.stanford.edu <mailto:srbare at slac.stanford.edu>>
> wrote:
> >>>
> >>>         All:____
> >>>
> >>>         __ __
> >>>
> >>>         We are wondering if others agree that the reported values for
> >>>         the W L3 and W L2 edges are *incorrect*. We recently noticed
> >>>         the following:____
> >>>
> >>>         __ __
> >>>
> >>>         The “Edge” – defined by the inflection point of the
> >>>         absorption edge step____
> >>>
> >>>         __ __
> >>>
> >>>         When using the Ir L_3 edge (11215.0 eV) as a calibration, the
> >>>         W L_3 - and L_2 -edges are *10203.4 eV* and *11542.4 eV*,
> >>>         respectively. ____
> >>>
> >>>         __ __
> >>>
> >>>         When using the Pt L_3 edge (11564.0 eV) as a calibration, the
> >>>         W L_3 - and L_2 -edges are *10203.3 eV* and *11542.4 eV*,
> >>>         respectively.____
> >>>
> >>>         __ __
> >>>
> >>>         These observations are thus different than the reported
> >>>         values of *10207.0 eV* and *11544.0 eV* for the L_3 and L_2
> >>>         edges, respectively.____
> >>>
> >>>         __ __
> >>>
> >>>         Thanks in advance for the discussion and feedback.____
> >>>
> >>>         __ __
> >>>
> >>>         __ __
> >>>
> >>>         Simon R Bare____
> >>>
> >>>         /Distinguished Scientist____/
> >>>
> >>>         /SSRL, MS69____/
> >>>
> >>>         /SLAC National Accelerator Lab____/
> >>>
> >>>         /2575 Sand Hill Road____/
> >>>
> >>>         /Menlo Park CA 94025____/
> >>>
> >>>         __ __
> >>>
> >>>         simon.bare at slac.stanford.edu
> >>>         <mailto:simon.bare at slac.stanford.edu>____
> >>>
> >>>         Ph: 650-926-2629____
> >>>
> >>>         __ __
> >>>
> >>>         <image001.png>
> >>>         ____
> >>>
> >>>         __ __
> >>>
> >>>         _______________________________________________
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> >>>
> >>>
> >>>     --
> >>>     --Matt Newville <newville at cars.uchicago.edu
> >>>     <http://cars.uchicago.edu>> 630-252-0431
> >>>     <W.prj>
> >>>     <CalibratedFoils2013.prj>
> >>>     <FeCu_AuPb.prj>
> >>>     _______________________________________________
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> >>
> >> --
> >> --Matt Newville <newville at cars.uchicago.edu
> >> <http://cars.uchicago.edu>> 630-252-0431
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