[Ifeffit] Energy Resolution

Thu May 10 10:15:59 CDT 2018

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-bounces at millenia.cars.aps.anl.gov] Im Auftrag von Robert Meulenberg
Gesendet: Mittwoch, 9. Mai 2018 14:55
An: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
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.meulenberg at maine.edu <mailto:robert.meulenberg at maine.edu> 

On Wed, May 9, 2018 at 3:24 AM, Julian Ehwald <jehwald at gmail.com <mailto:jehwald at 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-bounces at millenia.cars.aps.anl.gov <mailto:ifeffit-bounces at millenia.cars.aps.anl.gov> ] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov <mailto:ifeffit at 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: 312.567.3498            Fax: 312.567.3494
segre at iit.edu <mailto:segre at iit.edu>    http://phys.iit.edu/~segre   segre at debian.org <mailto:segre at debian.org> 
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