[Ifeffit] common mono crystals

Matt Newville newville at cars.uchicago.edu
Wed Dec 1 09:58:12 CST 2004


Bruce,

Diamond 111 is fairly common (I'd guess more common than anything
but Si), and you probably meant Si(220) instead of (200).  InSb is
probably the next most common for the 1 to 2 keV range.  I think
the others are not so common for XAFS as the energy bandpass is
too wide.  Also, Si at room temperature is slightly different than
at LN2 temperature....

But also needed for that calculation is the number of motor steps
or encoder steps per angular unit.  OK, angular unit is probably
most commonly in degrees, but I wouldn't assume that it's never in
radians. For steps per angular unit, it's usually a many thousand 
steps per degree but it can be pretty much any number.  

So, it's complicated to convert 'steps' to eV.  Personally, I'm
comfortable insisting that the beamline/facility provide energy in
eV, keV, Angstroms. or at least angle in degrees with the
monochromator lattice constant clearly given.  

That is, I don't think this should be athena's job.  I think it
would be better to have more support for beamline-specific
formats.  Then, if some particular beamline saves the "energy"  
in nanoJoules or milliradians that could be marked and
auto-converted, but I don't think athena should worry about what
kind of monochromator was used or steps-per-degree.

The data in the Lytle archive is possibly a special case, because
it's commonly available.  It's usually well marked for conversion
to energy, but the data is poorly documented and spotty in quality
and it's often hard to tell what exactly the columns are (e-yield
v. fluorescence, for example).  That can make it hard to asses the
quality of the data (is self-absorption a problem, etc).  I do use
it sometimes, but the data is not all that reliable.

Having a more complete and well-maintained database of data,
including some of the data from the Lytle database would be nice.  
Any volunteers to work on that?

--Matt




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