Dear RG community!
I am obtaining very weird peaks on the XRD pattern. There is a shoulder on the left side of the peak looking like a step. Arrow on the picture. It is about 2-3% of the Ka1 peak intensity. It appears before every peak with constant 2-3% of relative intensity on the constant distance. And I have no idea what it could be. It doesn't fit with any known Cu Ka satellite spectrum. Doesn't match with potential W emission from the tube.
This is perfectly flat LaB6 powder standard confirmed on the other diffractometer. Al2O3 standard gives the same artifact. The XRD is Bruker D8. Optics is in reflection geometry with copper X-ray tube, no monochromator, 0.2 mm motorized divergence slit, incident and receiving 2.5 degree Soller slits, Ni filter, PSD detector.
Any ideas what is the origin of this shoulder? Or what more important, how to eliminate it?
Thank you!
Dear Robert Möckel and Gerhard Martens , thanks a lot for your help. It turned out to be tube tails and Kb absorption edge artifacts. The such prominent tube tails are not usual indeed. I found out later that the tube is degrading very quickly. It is only 3 years old, has only 2 years of heavy use and now produces only 10% of X-rays in comparison to three years ago state. Apparently, there is a major defect from the factory. May be this causes such strong tube tails as well.
Dear Ivan A. Trussov ,
curious.
Maybe some issues with adjustment, e.g . non-parallel slit(s)....
Just an idea: you may remove slits and then replace them; they might not be snapped at the right position....
good luck
As Gerhard Martens mentioned, the issue might be due to either instrument or some issue while integrating the XRD image to intensity vs 2 thata
If your diffractometer is not equipped with a k-beta filter??? it could simple be the white spectrum of your tube. I see that on our Philips X-pert with a similar shape, but usually with much lower relative intensity. Even if a K-beta filter is in place, without a monochromator you usually do get a white spectrum tail. As Gerhard Martens mentioned, there's likey some misalignment
...or.....you may accidentally have interchanged the front and back side when inserting the slit module...
As I mentioned in previous comments, this peak splitting could be also . Because of the XRD profile I have realized that your sample is nanoparticle . The shape of the shoulder and tail of the peak from the left indicates consistent FWHM.
This effect is due to instrumental emission spectra impurity (called tube tails & ka satellite) and also present when K-beta filter is used. In attached figure one can see that Ni filter reduce K-beta component but there is small kink in spectra above Ni-K edge absorption wavelength. This kink starts at wavelength smaller than K-alfa1,2 doublet (~1.54 A) of Cu target and therefore in XRD pattern its effects always appears towards lower 2theta side of Bragg peak. This is probably the reason of such LaB6 spectra. More details in many XRD books e.g. B. D. Cullity.
Dear Ashok Bhakar ,
you are right. One could think that it is due to the Ni K-edge. But a rough estimation of photon energy of the low 2theta cut-off at about 2theta~30° will give value of about 8,15keV. This is far from Ni K-edge energy of 8,33keV. Thus the Ni filter has apparently nothing to do with that phenomenon.
The high 2theta cut-off is at about 8,0keV.
Such instrumental effect is commonly observed (mainly with higher intensity Bragg peaks) in lab sources, but quite pronounced in your case. Its modelling might not be easily possible with many programs, although this effect is accounted in refinement by some experts of this field as in attached tube tails jpg file. Further details available at following sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4849620/
https://nvlpubs.nist.gov/nistpubs/jres/109/1/j91che.pdf
LYNXEYE XE detectors suppress this effect, one can see its manual for working.
Specimen error may cause such effect (at lower 2theta side of paek) but in your case it may not be the main reason because XRD peaks are distorted at both side of Bragg angle similar to tube tails & Ka satellite.
Jupp, that's a tubetail, although quite strong?!? Is it a new tube??
check e.g. https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=905010
The BGMN/Profex software is able to recalculate this from measured data.
Dear all,
I am not really convinced that this is due to the tube tail effect:
a) the XRD pattern presented by Ashok Bhakar and Robert Möckel are in logarithmic scale,
b) the footprint of Ivan A. Trussov 's pattern is much boader and is in linear scale,
c) I have never seen a Cu K alpha-3 satellite peak in my former spectral (WDS) measurements from a Cu tube
Dear Robert Möckel and Gerhard Martens , thanks a lot for your help. It turned out to be tube tails and Kb absorption edge artifacts. The such prominent tube tails are not usual indeed. I found out later that the tube is degrading very quickly. It is only 3 years old, has only 2 years of heavy use and now produces only 10% of X-rays in comparison to three years ago state. Apparently, there is a major defect from the factory. May be this causes such strong tube tails as well.
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