Re: [Ifeffit] Energy resolution issue [DLM=For-Official-Use-Only]

[Matt Newville]

Hi Bernt,

Sorry for the trouble.  We've had a few similar questions here over the
past few months, and some very recently.   Is the Energy channel for your
raw data in keV? If so, and if you're converting it to Athena-friendly
ASCII-readable anyway, try putting the Energy in eV.



On Thu, Apr 11, 2019 at 5:57 AM JOHANNESSEN, Bernt 
wrote:

> Hi there,
>
>
> I'm using a Demeter 0.9.26 download to display data in Athena. My raw data
> was converted into ascii readable format retaining a measured 0.25 eV step
> size through the XANES region. However, Athena seems to inexplicably change
> the plotted step size to 1.00 eV. I've reinstalled Demeter/Athena without
> any luck. I also have an older version of Athena (0.8.056) that can display
> the data with the correct / measured step size of 0.25 eV without any
> issues. Any idea why Demeter is messing up my energy resolution when I have
> not changed a single default parameter?
>
>
> Cheers, Bernt
>
>
>
>
>
> *Dr. Bernt Johannessen*
>
>
> *Senior Scientist - XASAustralian Synchrotron*
>
>
>
> *TelEmailWeb*
>
> +61 3 8540 4240
> ber...@ansto.gov.au
> www.ansto.gov.au
>
> *[image: fb]*
> 
>  *[image: tw]*
> 
>  *[image: ln]*  *[image: yt]*
> 
>
> [image: ansto]
>
>
>
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--Matt
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Re: [Ifeffit] Energy Resolution

[Lorenzo Stievano]

  
  
Hi Julian,
Carlo is completely right about the S0^2, and the common way to
  handle it (measure it for a standard and then transfer it, keeping
  it fixed, to the other measured materials).
I would just like to add that it is preferable that the standard
  and the materials have similar thickness (absorption coefficient)
  and especially good homogeneity. In fact, while the first one has
  an important influence on the amplitude of the EXAFS oscillations
  (especially when you deal with thick samples at low energies), the
  second one might also induce you in a wrong evaluation of the real
  value of the edge jump and thus of the amplitude of the
  oscillations (with inhomogenoeus samples, you may obtain edge
  jumps of acceptable values with attenuated oscillations).

This just to stress that sample preparation is really extremely
  important also to obtain a correct evaluation of the S0^2 from a
  reference compound.
Yours, Lorenzo




On 10/05/2018 18:06, Carlo Segre wrote:


  
  Hi Julian:
  
  
  I would be happy to help with this.  Let me answer briefly on the
  list and afterward, if you like, just contact me privately and we
  can discuss in more depth.
  
  
  S02 is a property of the absorbing atom and is due to the change
  in electronic energy levels because of the present  of a core hole
  after the photoabsorption event.  It is usually considered to be
  transferable from material to material with the same element
  because it is really a local property.  However, in practice it
  does depend on the type of compound you are measuring and the
  beamline as well as the type of measurement you are making
  (transmission, fluorescence).  All of these factors can masquerade
  a amplitude reduction factor.
  
  
  What I do in practice is to measure a standard which has the same
  local environment and fit the EXAFS with the known structure to
  extract an S02 which I then use transferably.
  
  
  As for your question about delta R.  If your EXAFS cannot be fit
  using an isotropic expansion model (not always the best way
  anyway) then you most likely need to make the delta R parameters
  independent.  There is absolutely no reason to correlate a shorter
  path with a longer path even if it is the same element, unless you
  are using a known structure model out of which you are trying to
  extract specific parameters.
  
  
  Hope this helps.
  
  
  Carlo
  
  
  On Thu, 10 May 2018, Julian Ehwald wrote:
  
  
  Hi Carlo


Thank you for your answer. I have completely different question
as well: I

just started using Artemis, and have a question regarding the
amplitude

reduction factor: I use different So^2 for different elements,
correct? If I

start fitting and have paths involving the same kind of atom but
once at

distance 2A, and once maybe 3A, is this then the same So^2 or am
I supposed

to model the behaviour of So^2 somehow?

Similar for \Delta R: If I don?t have a nice simple cubic
structure and

can?t use isotropic expansion similar like alpha*R_eff, what
would be a

smart(or physically correct) way to connect \Delta R (as well as
sigma^2)

for the same element for different distances? The material I am
looking at

is Li2O2 and Li2IrO3, which don?t have a very simple structure.


I am aware that maybe I am asking a bit much, but if you could
help me in

any way I would be very delighted.


Best, Julian


-Ursprüngliche Nachricht-

Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov]
Im Auftrag

von Carlo Segre

Gesendet: Sonntag, 6. Mai 2018 01:07

An: XAFS Analysis using Ifeffit


Betreff: Re: [Ifeffit] Energy Resolution



Hi Julian:


With an edge energy of 543 eV, your monochromator resolution
should be at

least 0.1 eV.  If you are interested in XANES, you need to take
data at this

resolution or maybe even better.  ONce past the edge, there is
no need to

keep that step size.  If your beamline permits an EXAFS-type
step scan with

steps in k-space, you want to use a dk of 0.05 which is what
IFEFFIT

interpolates to.  Smaller step sizes are not really useful

Re: [Ifeffit] Energy Resolution

[Carlo Segre]

Hi Julian:

I would be happy to help with this.  Let me answer briefly on the list and 
afterward, if you like, just contact me privately and we can discuss in 
more depth.


S02 is a property of the absorbing atom and is due to the change in 
electronic energy levels because of the present  of a core hole after the 
photoabsorption event.  It is usually considered to be transferable from 
material to material with the same element because it is really a local 
property.  However, in practice it does depend on the type of compound you 
are measuring and the beamline as well as the type of measurement you are 
making (transmission, fluorescence).  All of these factors can masquerade 
a amplitude reduction factor.


What I do in practice is to measure a standard which has the same local 
environment and fit the EXAFS with the known structure to extract an S02 
which I then use transferably.


As for your question about delta R.  If your EXAFS cannot be fit using an 
isotropic expansion model (not always the best way anyway) then you most 
likely need to make the delta R parameters independent.  There is 
absolutely no reason to correlate a shorter path with a longer path even 
if it is the same element, unless you are using a known structure model 
out of which you are trying to extract specific parameters.


Hope this helps.

Carlo

On Thu, 10 May 2018, Julian Ehwald wrote:


Hi Carlo

Thank you for your answer. I have completely different question as well: I
just started using Artemis, and have a question regarding the amplitude
reduction factor: I use different So^2 for different elements, correct? If I
start fitting and have paths involving the same kind of atom but once at
distance 2A, and once maybe 3A, is this then the same So^2 or am I supposed
to model the behaviour of So^2 somehow?
Similar for \Delta R: If I don?t have a nice simple cubic structure and
can?t use isotropic expansion similar like alpha*R_eff, what would be a
smart(or physically correct) way to connect \Delta R (as well as sigma^2)
for the same element for different distances? The material I am looking at
is Li2O2 and Li2IrO3, which don?t have a very simple structure.

I am aware that maybe I am asking a bit much, but if you could help me in
any way I would be very delighted.

Best, Julian

-Ursprüngliche Nachricht-
Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit 
Betreff: Re: [Ifeffit] Energy Resolution


Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at
least 0.1 eV.  If you are interested in XANES, you need to take data at this
resolution or maybe even better.  ONce past the edge, there is no need to
keep that step size.  If your beamline permits an EXAFS-type step scan with
steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
interpolates to.  Smaller step sizes are not really useful.

Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:


Dear all,



This might be a very general question, but: I was wondering what
energy resolution you typically use at beamlines to obtain your raw data

for exafs.

Since we have limited Beamtime only and other experiments that we want
to carry out, I was wondering what kind of resolution is common. Or
differently: Is it predictable what happens if I for example change
from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV
above Oxygen K, if that is of relevance.

Best, Julian




--
Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
Department of Chemistry Director, Center for Synchrotron Radiation Research
and Instrumentation Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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--
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Interim Chair, Department of Chemistry
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
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Re: [Ifeffit] Energy Resolution

[Julian Ehwald]

Hi Carlo

Thank you for your answer. I have completely different question as well: I
just started using Artemis, and have a question regarding the amplitude
reduction factor: I use different So^2 for different elements, correct? If I
start fitting and have paths involving the same kind of atom but once at
distance 2A, and once maybe 3A, is this then the same So^2 or am I supposed
to model the behaviour of So^2 somehow?
Similar for \Delta R: If I don’t have a nice simple cubic structure and
can’t use isotropic expansion similar like alpha*R_eff, what would be a
smart(or physically correct) way to connect \Delta R (as well as sigma^2)
for the same element for different distances? The material I am looking at
is Li2O2 and Li2IrO3, which don’t have a very simple structure.

I am aware that maybe I am asking a bit much, but if you could help me in
any way I would be very delighted. 

Best, Julian

-Ursprüngliche Nachricht-
Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit 
Betreff: Re: [Ifeffit] Energy Resolution


Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at
least 0.1 eV.  If you are interested in XANES, you need to take data at this
resolution or maybe even better.  ONce past the edge, there is no need to
keep that step size.  If your beamline permits an EXAFS-type step scan with
steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
interpolates to.  Smaller step sizes are not really useful.

Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:

> Dear all,
>
>
>
> This might be a very general question, but: I was wondering what 
> energy resolution you typically use at beamlines to obtain your raw data
for exafs.
> Since we have limited Beamtime only and other experiments that we want 
> to carry out, I was wondering what kind of resolution is common. Or
> differently: Is it predictable what happens if I for example change 
> from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV 
> above Oxygen K, if that is of relevance.
>
> Best, Julian
>
>

--
Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
Department of Chemistry Director, Center for Synchrotron Radiation Research
and Instrumentation Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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Re: [Ifeffit] Energy Resolution

[Julian Ehwald]

Hi Rob,

 

Thank you for your answer. I am aware of this problem, however they want me to 
try anyway so I’ll do my best and hope to get at least to k=10.5 or something. 
Anyway, I have completely different question as well: I just started using 
Artemis, and have a question regarding the amplitude reduction factor: I use 
different So^2 for different elements, correct? If I start fitting and have 
paths involving the same kind of atom but once at distance 2A, and once maybe 
3A, is this then the same So^2 or am I supposed to model the behaviour of So^2 
somehow?
Similar for \Delta R: If I don’t have a nice simple cubic structure and can’t 
use isotropic expansion similar like alpha*R_eff, what would be a smart(or 
physically correct) way to connect \Delta R (as well as sigma^2) for the same 
element for different distances? The material I am looking at is Li2O2 and 
Li2IrO3, which don’t have a very simple structure.

I am aware that maybe I am asking a bit much, but if you could help me in any 
way I would be very delighted. 

 

Best, Julian

 

Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] Im Auftrag von 
Robert Meulenberg
Gesendet: Mittwoch, 9. Mai 2018 14:55
An: XAFS Analysis using Ifeffit 
Betreff: Re: [Ifeffit] Energy Resolution

 

Julian,

 

Keep in mind that to get to k=12, you will need to go out to ~1100 eV.  At 
these energies, you will encounter just about every 1st row transition metal L 
edge, and a handful of other M-edges for heavier elements.  So if you have 
anything else in your sample, EXAFS will probably not be possible.  That is 
usually why people don't try to do EXAFS analysis at the soft x-ray energies.

 

Regards,

 

Rob

 

 

 




Robert W. Meulenberg
Associate Professor of Physics
Laboratory for Surface Science and Technology
Department of Physics and Astronomy
University of Maine
Orono, ME 04469
phone: 207-581-2245
email: robert.meulenb...@maine.edu <mailto:robert.meulenb...@maine.edu> 

 

On Wed, May 9, 2018 at 3:24 AM, Julian Ehwald mailto:jehw...@gmail.com> > wrote:

Hi Carlo

Thank you very much for your answer! If you say it is sufficient to use
dk=0.05, that means I would be able to collect a full EXAFS spectra (k=0 to
12) in only 250 datapoints? That would save us a lot of time!

Best, Julian

-Ursprüngliche Nachricht-
Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov 
<mailto:ifeffit-boun...@millenia.cars.aps.anl.gov> ] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit mailto:ifeffit@millenia.cars.aps.anl.gov> >
Betreff: Re: [Ifeffit] Energy Resolution



Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at
least 0.1 eV.  If you are interested in XANES, you need to take data at this
resolution or maybe even better.  ONce past the edge, there is no need to
keep that step size.  If your beamline permits an EXAFS-type step scan with
steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
interpolates to.  Smaller step sizes are not really useful.

Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:

> Dear all,
>
>
>
> This might be a very general question, but: I was wondering what 
> energy resolution you typically use at beamlines to obtain your raw data
for exafs.
> Since we have limited Beamtime only and other experiments that we want 
> to carry out, I was wondering what kind of resolution is common. Or
> differently: Is it predictable what happens if I for example change 
> from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV 
> above Oxygen K, if that is of relevance.
>
> Best, Julian
>
>

--
Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
Department of Chemistry Director, Center for Synchrotron Radiation Research
and Instrumentation Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
se...@iit.edu <mailto:se...@iit.edu>http://phys.iit.edu/~segre   
se...@debian.org <mailto:se...@debian.org> 
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Re: [Ifeffit] Energy Resolution

[Robert Meulenberg]

Julian,

Keep in mind that to get to k=12, you will need to go out to ~1100 eV.  At
these energies, you will encounter just about every 1st row transition
metal L edge, and a handful of other M-edges for heavier elements.  So if
you have anything else in your sample, EXAFS will probably not be
possible.  That is usually why people don't try to do EXAFS analysis at the
soft x-ray energies.

Regards,

Rob




Robert W. Meulenberg
Associate Professor of Physics
Laboratory for Surface Science and Technology
Department of Physics and Astronomy
University of Maine
Orono, ME 04469
phone: 207-581-2245
email: robert.meulenb...@maine.edu

On Wed, May 9, 2018 at 3:24 AM, Julian Ehwald  wrote:

> Hi Carlo
>
> Thank you very much for your answer! If you say it is sufficient to use
> dk=0.05, that means I would be able to collect a full EXAFS spectra (k=0 to
> 12) in only 250 datapoints? That would save us a lot of time!
>
> Best, Julian
>
> -Ursprüngliche Nachricht-
> Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] Im Auftrag
> von Carlo Segre
> Gesendet: Sonntag, 6. Mai 2018 01:07
> An: XAFS Analysis using Ifeffit 
> Betreff: Re: [Ifeffit] Energy Resolution
>
>
> Hi Julian:
>
> With an edge energy of 543 eV, your monochromator resolution should be at
> least 0.1 eV.  If you are interested in XANES, you need to take data at
> this
> resolution or maybe even better.  ONce past the edge, there is no need to
> keep that step size.  If your beamline permits an EXAFS-type step scan with
> steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
> interpolates to.  Smaller step sizes are not really useful.
>
> Carlo
>
> On Sat, 5 May 2018, Julian Ehwald wrote:
>
> > Dear all,
> >
> >
> >
> > This might be a very general question, but: I was wondering what
> > energy resolution you typically use at beamlines to obtain your raw data
> for exafs.
> > Since we have limited Beamtime only and other experiments that we want
> > to carry out, I was wondering what kind of resolution is common. Or
> > differently: Is it predictable what happens if I for example change
> > from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV
> > above Oxygen K, if that is of relevance.
> >
> > Best, Julian
> >
> >
>
> --
> Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
> Department of Chemistry Director, Center for Synchrotron Radiation Research
> and Instrumentation Illinois Institute of Technology
> Voice: 312.567.3498Fax: 312.567.3494
> se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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Re: [Ifeffit] Energy Resolution

[Julian Ehwald]

Hi Carlo

Thank you very much for your answer! If you say it is sufficient to use
dk=0.05, that means I would be able to collect a full EXAFS spectra (k=0 to
12) in only 250 datapoints? That would save us a lot of time!

Best, Julian

-Ursprüngliche Nachricht-
Von: Ifeffit [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit 
Betreff: Re: [Ifeffit] Energy Resolution


Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at
least 0.1 eV.  If you are interested in XANES, you need to take data at this
resolution or maybe even better.  ONce past the edge, there is no need to
keep that step size.  If your beamline permits an EXAFS-type step scan with
steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
interpolates to.  Smaller step sizes are not really useful.

Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:

> Dear all,
>
>
>
> This might be a very general question, but: I was wondering what 
> energy resolution you typically use at beamlines to obtain your raw data
for exafs.
> Since we have limited Beamtime only and other experiments that we want 
> to carry out, I was wondering what kind of resolution is common. Or
> differently: Is it predictable what happens if I for example change 
> from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV 
> above Oxygen K, if that is of relevance.
>
> Best, Julian
>
>

--
Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
Department of Chemistry Director, Center for Synchrotron Radiation Research
and Instrumentation Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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Re: [Ifeffit] Energy Resolution

[Carlo Segre]

Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at 
least 0.1 eV.  If you are interested in XANES, you need to take data at 
this resolution or maybe even better.  ONce past the edge, there is no 
need to keep that step size.  If your beamline permits an EXAFS-type step 
scan with steps in k-space, you want to use a dk of 0.05 which is what 
IFEFFIT interpolates to.  Smaller step sizes are not really useful.


Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:


Dear all,



This might be a very general question, but: I was wondering what energy
resolution you typically use at beamlines to obtain your raw data for exafs.
Since we have limited Beamtime only and other experiments that we want to
carry out, I was wondering what kind of resolution is common. Or
differently: Is it predictable what happens if I for example change from
steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV above Oxygen
K, if that is of relevance.

Best, Julian




--
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Interim Chair, Department of Chemistry
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498Fax: 312.567.3494
se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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[Ifeffit] Energy Resolution

[Julian Ehwald]

Dear all,

 

This might be a very general question, but: I was wondering what energy
resolution you typically use at beamlines to obtain your raw data for exafs.
Since we have limited Beamtime only and other experiments that we want to
carry out, I was wondering what kind of resolution is common. Or
differently: Is it predictable what happens if I for example change from
steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV above Oxygen
K, if that is of relevance.

Best, Julian

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Re: [Ifeffit] energy resolution

[Bruce Ravel]

On 04/20/2015 12:01 PM, Lisa Bovenkamp wrote:

Now here is question 1:
What is the combination of the two profiles in the Athena peak fitting routine 
for the Pseudo-Voigt?


Hi Lisa,

Athena uses Ifeffit for this.  Ifeffit's pseudo-Voight function is 
implemented here:


 https://github.com/newville/ifeffit/blob/master/src/lib/conv_lor.f#L314

(Larch's is explained here: 
http://xraypy.github.io/xraylarch/fitting/lineshapes.html)


In Athena, gamma is the mixing parameter for the pseudo-Voight.

That said, this might not be doing quite what you are looking for. 
Ifeffit's implementation uses the same width for both functions (as does 
Larch), which does not seem to be what you are asking for.


I suppose you could try using two lineshapes, one Gaussian and one 
Lorentzian, which share a value for the centroid.  That is possible in 
Athena as long as you don't float the centroids.  While floating a 
common centroid is possible in both Ifeffit and Larch, there is no way 
to indicate that in Athena.  I'm not sure off the top of my head how to 
interpret the amplitudes in that situation to extract a value equivalent 
to gamma.


Perhaps Athena isn't the right tool for the job?  Or perhaps you can 
figure out something that does what you want using either Ifeffit or 
(preferably!) Larch?  In that case, let me know and I'll see about 
including it in Athena.


B

--
 Bruce Ravel   bra...@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Science Group at NSLS-II
 Building 535A
 Upton NY, 11973

 Homepage:http://bruceravel.github.io/home/
 Software:https://github.com/bruceravel
 Demeter: http://bruceravel.github.io/demeter/
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Re: [Ifeffit] energy resolution

[Lisa Bovenkamp]

Hello all.
I am getting confused with different comments how to determine the energy 
resolution
of an XAS beamline.
I think using peak fitting to determine the line width is a reasonable method.
The basis of a XAS peak is the Voigt profile (a combination of a Lorenzian and 
Gaussian)
The width of the Lorenzian equals the natural line width
while the width of the Gaussian represents the experimental line width and some 
features
Now here is question 1: 
What is the combination of the two profiles in the Athena peak fitting routine 
for the Pseudo-Voigt?
Question 2:
Is the sigma (Gaussian width) that delta E that represents
the resolution - (E /delta E) ?

Using a different program (Igor Pro) to determine 
the width gives different results because can only 
use a simple combination of Lorentz and Gauss (1:1).

Thanks.
Lisa



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Re: [Ifeffit] energy resolution

[Matthew Marcus]

The reason I mentioned using transmission is that you could get to a true 
back-reflection condition that way, thus removing sensitivity to incidence 
angle.  Another possibility for detecting the reflection is to look for a peak 
in I0, caused by the back-reflecting beam going back into the I0 chamber.
mam

On 5/5/2010 11:49 AM, Frenkel, Anatoly wrote:

This is a quote from Joseph Dvorak' report on energy resolution measurements at 
the NSLS beamlines:
 
The energy resolution was measured as follows. A Si 220 crystal was used as an analyzer crystal.


This was placed in the hutch in near back reflection condition (87 deg inc). 
The reflected x-rays were

detected with a Si photodiode. Oriented as such, the analyzer crystal reflects 
at its fundamental (3233 eV)

and all higher order reflections (440, 660, ...). The beamline monochromator 
was then scanned

successively through the various reflections of the analyzer crystal. Since the 
energy bandpass of the

analyzer crystal in back reflection is very narrow compared to the fundamental 
of the beamline

monochromator (true for all the higher order analyzer crystal reflections, and 
possibly true for the

fundamental depending on the monochromator crystal), a measurement of the width 
of the reflected beam

gives a direct measurement of the energy resolution. The second monochromator 
crystal was set to full

tune.

Anatoly

 



From: ifeffit-boun...@millenia.cars.aps.anl.gov on behalf of Matthew
Sent: Wed 5/5/2010 2:42 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] energy resolution



That method only works at one energy, and assumes something about the width of 
the V2O5 feature.  Another possible method might be
to measure, in back-reflection, a high-order Bragg reflection from a Si 
crystal.  For instance, the 555 reflection would be at
9.9keV.  If you put up a 111 Si crystal and did a transmission scan, maybe you 
could detect the reflection as a transmission dip.
You would then play with the orientation of the crystal so that the energy at 
which this dip occurred was as low as possible,
meaning that you were at back-reflection.  This condition is useful because it 
gives the least sensitivity to beam divergence.  You
could then calculate the Darwin broadening of the 555 reflection to correct the 
observed value.  By choosing different reflections,
you could measure the resolution at different energies.  Of course, I haven't 
tried this myself.
mam
- Original Message -
From: "Bruce Ravel" 
To: ; "XAFS Analysis using Ifeffit" 

Sent: Wednesday, May 05, 2010 11:19 AM
Subject: Re: [Ifeffit] energy resolution



On Wednesday 05 May 2010 02:12:38 pm M Ceolin wrote:

Hi all.

I would like to know if anyone knows an experimental method to determine
 the energy resolution in the XANES region of a XAS spectrum. I do not
 explored the previous entries in the list so I beg you pardon if it was
 already discussed. Thank you for the information.

Hi Marcelo,

A few years back the folks at the APS used the method described about
half-way down the page at:

 http://xafs.org/APSXAFS/APS_XOR_Eval

One example evaluation is shown at

 http://xafs.org/APSXAFS/APS_XOR_Eval/20BM/EResolution

HTH,
B


--

Bruce Ravel   bra...@bnl.gov

National Institute of Standards and Technology
Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
Building 535A
Upton NY, 11973

My homepage:http://xafs.org/BruceRavel
EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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Re: [Ifeffit] energy resolution

[Frenkel, Anatoly]

This is a quote from Joseph Dvorak' report on energy resolution measurements at 
the NSLS beamlines:
 
The energy resolution was measured as follows. A Si 220 crystal was used as an 
analyzer crystal.

This was placed in the hutch in near back reflection condition (87 deg inc). 
The reflected x-rays were

detected with a Si photodiode. Oriented as such, the analyzer crystal reflects 
at its fundamental (3233 eV)

and all higher order reflections (440, 660, ...). The beamline monochromator 
was then scanned

successively through the various reflections of the analyzer crystal. Since the 
energy bandpass of the

analyzer crystal in back reflection is very narrow compared to the fundamental 
of the beamline

monochromator (true for all the higher order analyzer crystal reflections, and 
possibly true for the

fundamental depending on the monochromator crystal), a measurement of the width 
of the reflected beam

gives a direct measurement of the energy resolution. The second monochromator 
crystal was set to full

tune.

Anatoly

 


From: ifeffit-boun...@millenia.cars.aps.anl.gov on behalf of Matthew
Sent: Wed 5/5/2010 2:42 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] energy resolution



That method only works at one energy, and assumes something about the width of 
the V2O5 feature.  Another possible method might be
to measure, in back-reflection, a high-order Bragg reflection from a Si 
crystal.  For instance, the 555 reflection would be at
9.9keV.  If you put up a 111 Si crystal and did a transmission scan, maybe you 
could detect the reflection as a transmission dip.
You would then play with the orientation of the crystal so that the energy at 
which this dip occurred was as low as possible,
meaning that you were at back-reflection.  This condition is useful because it 
gives the least sensitivity to beam divergence.  You
could then calculate the Darwin broadening of the 555 reflection to correct the 
observed value.  By choosing different reflections,
you could measure the resolution at different energies.  Of course, I haven't 
tried this myself.
mam
- Original Message -
From: "Bruce Ravel" 
To: ; "XAFS Analysis using Ifeffit" 

Sent: Wednesday, May 05, 2010 11:19 AM
Subject: Re: [Ifeffit] energy resolution


> On Wednesday 05 May 2010 02:12:38 pm M Ceolin wrote:
>> Hi all.
>>
>> I would like to know if anyone knows an experimental method to determine
>>  the energy resolution in the XANES region of a XAS spectrum. I do not
>>  explored the previous entries in the list so I beg you pardon if it was
>>  already discussed. Thank you for the information.
>
> Hi Marcelo,
>
> A few years back the folks at the APS used the method described about
> half-way down the page at:
>
>  http://xafs.org/APSXAFS/APS_XOR_Eval
>
> One example evaluation is shown at
>
>  http://xafs.org/APSXAFS/APS_XOR_Eval/20BM/EResolution
>
> HTH,
> B
>
>
> --
>
> Bruce Ravel   bra...@bnl.gov
>
> National Institute of Standards and Technology
> Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
> Building 535A
> Upton NY, 11973
>
> My homepage:http://xafs.org/BruceRavel
> EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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Re: [Ifeffit] energy resolution

[Matthew]

That method only works at one energy, and assumes something about the width of the V2O5 feature.  Another possible method might be 
to measure, in back-reflection, a high-order Bragg reflection from a Si crystal.  For instance, the 555 reflection would be at 
9.9keV.  If you put up a 111 Si crystal and did a transmission scan, maybe you could detect the reflection as a transmission dip. 
You would then play with the orientation of the crystal so that the energy at which this dip occurred was as low as possible, 
meaning that you were at back-reflection.  This condition is useful because it gives the least sensitivity to beam divergence.  You 
could then calculate the Darwin broadening of the 555 reflection to correct the observed value.  By choosing different reflections, 
you could measure the resolution at different energies.  Of course, I haven't tried this myself.

   mam
- Original Message - 
From: "Bruce Ravel" 

To: ; "XAFS Analysis using Ifeffit" 

Sent: Wednesday, May 05, 2010 11:19 AM
Subject: Re: [Ifeffit] energy resolution



On Wednesday 05 May 2010 02:12:38 pm M Ceolin wrote:

Hi all.

I would like to know if anyone knows an experimental method to determine
 the energy resolution in the XANES region of a XAS spectrum. I do not
 explored the previous entries in the list so I beg you pardon if it was
 already discussed. Thank you for the information.


Hi Marcelo,

A few years back the folks at the APS used the method described about
half-way down the page at:

 http://xafs.org/APSXAFS/APS_XOR_Eval

One example evaluation is shown at

 http://xafs.org/APSXAFS/APS_XOR_Eval/20BM/EResolution

HTH,
B


--

Bruce Ravel   bra...@bnl.gov

National Institute of Standards and Technology
Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
Building 535A
Upton NY, 11973

My homepage:http://xafs.org/BruceRavel
EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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Re: [Ifeffit] energy resolution

[Bruce Ravel]

On Wednesday 05 May 2010 02:12:38 pm M Ceolin wrote:
> Hi all.
>  
> I would like to know if anyone knows an experimental method to determine
>  the energy resolution in the XANES region of a XAS spectrum. I do not
>  explored the previous entries in the list so I beg you pardon if it was
>  already discussed. Thank you for the information.
 
Hi Marcelo,

A few years back the folks at the APS used the method described about
half-way down the page at: 

  http://xafs.org/APSXAFS/APS_XOR_Eval

One example evaluation is shown at

  http://xafs.org/APSXAFS/APS_XOR_Eval/20BM/EResolution

HTH,
B


-- 

 Bruce Ravel   bra...@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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[Ifeffit] energy resolution

[M Ceolin]

Hi all.
 
I would like to know if anyone knows an experimental method to determine the 
energy resolution in the XANES region of a XAS spectrum.
I do not explored the previous entries in the list so I beg you pardon if it 
was already discussed.
Thank you for the information.
 
Marcelo


Prof. Dr. Marcelo Ceolin
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas
UNLP-CONICET
Diagonal 113 y 64
Casilla de Correo 16 (sucursal 4)
(B1906ZAA) La Plata
Argentina

Tel: +54-221-4257291 or 4257430 (int:156)
Fax: +54-221-4254642
e-mail: mceo...@inifta.unlp.edu.ar or mrceo...@yahoo.com.ar
WEB: http://www.inifta.unlp.edu.ar/investig/ceolin.htm



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