Dear Davide,
I assume the diffractometer type you are talking about is a
Bragg-Brentano diffractometer with flat sample.
Such a diffractometer commonly uses a ~ 1cm long footprint of the
electron beam onto the target (Cu, Co, Mo etc). Correspondingly the
detector is about a good cm wide as well. The purpose of the
Soller-collimator is to cut the primary beam into a group of parallel
slices along this 1 cm footprint on the source. Especially at lower
2Theta (5 to 20° 2Theta) this enhances the instrumental resolution /
reduces the asymmetry of the observed reflection profile.
Two effects cause this asymmetric broadening at lower 2Theta:
1) Any x-ray path that travels along the intended directions along the
soller collimator will still cause a Debye-Scherrer cone of diffracted
intensity. The broad detector will integrate the curved signal into a
single intensity at the nominal 2Theta position. As the parts of the
Debye-Scherrer cone to the side of the central position are
geometrically at a lower position, the detector will report this
intensity at a lower 2Theta. This effect is more prominent at lower
2Theta. Imagine a flat area detector, where you would see the complete
powder rings on the detector.
2) Without the Soller collimator, you will allow xray beams that will
travel "diagonally" across your sample. Lets assume the sample is
horizontal, and source and detector travel along a vertical arc. If we
now observe this from the top down, a beam that originates from the back
part of the electron footprint on the source diagonally onto the middle
of the sample and then on to the front section of the detector will
cause a differently oriented Debye-Scherrer cone than a beam path that
travels strictly in the plane defined by the Soller collimator. The
effect causes several Scherrer cones to appear on the detector the so
called "umbrella" effect.
Try a sample with much larger lattice parameter with Reflections at the
5 to 20° range and you should see a more drastic increase in the
asymmetry of the reflection profile at the low 2Theta side of your
reflections. In the data you presented you can actually see the effect
as well. The red line is (slightly) more asymmetric at the low 2Theta
side. at this "high" 2Theta the effect is mus less than at say 10°.
If all your samples have small lattice parameters, you will get away
without a Soller collimator and you will be able to enjoy the higher
intensity. For samples with higher lattice parameters, lower symmetry
you will have more reflection overlap even at low 2Theta. As always it
is a compromise between the desire for high intensities and small
angular resolution.
Hope this helps, yes I should have made / referenced a few schematic
drawings...
Best
Reinhard Neder
Am 14.11.24 um 08:52 schrieb davide.lev...@gmail.com:
Dear All,
I would like to know how the primary Soller Slits influence the
quality of the diffraction pattern, as from some test I did, I don't
see major differences in the peak shape. The use of these slits, on
the other hand, strongly cut the peak intensities.
Do you have any strong argument to use the primary Soller Slit for
qualitative and qualitative analysis?
Thank for your answer
Davide
Dr. Davide Levy, Ph.D.
X-ray diffraction lab. responsible , *TAU.nano*
*Jan Koum Center for Nanoscience and Nanotechnology*
*🌐**https://nano.tau.ac.il/ <https://nano.tau.ac.il/>*
📞+972-3- 6407815
📱0528698231
📧dav...@tau.ac.il
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Prof. Dr. Reinhard Neder
Kristallographie und Strukturphysik
Friedrich-Alexander-Universität Erlangen-Nürnberg
phone +49 9193 85 25 191
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