I assume you use the soller at the detector side, when you switch to grazing incidence. If the soller is strongly tilted with respect to the detector, you can get very bad readings. To check that you can repeat the 2theta scan of the incident beam. If there is a strong offset, this will be an indication of a misalignment of the soller.

Hmmm.  I have a D8 system, but I am not so familiar with the Grazing incidence measurement.   It sounds like your detector and source are well aligned.  Have you called the Bruker people?  Could it be an issue with your sample mounting?  Very curious.

Sorry I can't be more help.

Joe Deitzel

The sample holder was my first guess. The problem is the theta 2 theta scans are perfect. It seems the problem is in the detector side as I am using a gobel mirror which give me on the tube side a paralel beam. Kepp you updated with this

Which reflection are you looking for?

It seems to me it should be the 311 reflection (Tetab=28.05°, but incient angle at 2.81° is the surface is (100) oriented?)

In any case first you haveto find the Bragg condition by changing the angle of incidence. In this geometry also the azimuthal angle of the sample (rotation around the surface normal) is critical.

I assume you use the soller at the detector side, when you switch to grazing incidence. If the soller is strongly tilted with respect to the detector, you can get very bad readings. To check that you can repeat the 2theta scan of the incident beam. If there is a strong offset, this will be an indication of a misalignment of the soller.

Found the problem. My guess :Someone dropped the soller slit that went out of allign. Then he tried to allign the Brucker with a broken soller slit resulting in fact in a  huge missalignement of all angles. As soon as I succeed in reallign the soller slit everything went back in order.

The problem is that you use the Gobel on the Xray tube side you must use a soller slit (preferable a long one) on the detector side in order to keep the paralelism.

In 2014, nearly a century after the Braggs this shouldn't have really been such an enigma. Here is a visual of the shadow of the "soller slit" from BNL https://www.flickr.com/photos/85210325@N04/8646857294/in/set-72157635534175171 and another one from NMIF North Carolina - (https://www.flickr.com/photos/85210325@N04/9248173496/in/set-72157635534175171)

The reason it still persists as a challenge in nearly all  XRD facilities that I've visited in the recent 5 years is the lack of a quantitative real time 2D alignment tool. All of you are still "groping in the dark". I haven't even seen the use of photographic film (nearly extinct) to record the ubiquitous 2D XRD signal. Why so? Take off the "blind fold", now! It is quite a torture to endure in order to find the "real culprit", after considerable intellectual investment & exercise, the soller slit! 

This is how we verified the alignment conditions for the Bruker D8 at the TATA Institute Bengaluru aka The Indian Institute of Science, an old venerable institution of science and technology. See, no 0D blind-fold!

AXIS251432 - "Stand alone", 32um, 25mm diameter, 8-16Bit, 30-60fps 2D Real Time Bragg XRD Microscope attachment: https://www.flickr.com/photos/85210325@N04/13620538183/in/set-72157632729013664

Looking the tiger in the eye! Staring the main beam in the face: https://www.flickr.com/photos/85210325@N04/15336978941/

Si powder standard with clear evidence of preferred orientation of sample due to prep/loading: https://www.flickr.com/photos/85210325@N04/15340063112/

Corundum standard powder: https://www.flickr.com/photos/85210325@N04/15418209755/

Check out these discussions when convenient to fully get rid of the spatial "blind fold" avoiding "withdrawal" symptoms:-)

1. LinkedIn: https://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=5810700387807698945&goback=%2Egpa_2683600_1_*2_*2_*2_true_cad%2Egmp_2683600%2Egde_2683600_member_5923356035560534016%2Egna_2683600%2Egmp_2683600

2. Research Gate: https://www.researchgate.net/post/Bloody_Murder_Why_is_there_nearly_such_a_visceral_response_to_any_disruption_to_alignment_of_existing_diffractometers_by_XRD_users_technicians

Bottom Line: Did your diffractograms change after the final alignment adjustments?

Did you expect the nature of the Bragg profile to change due to the difference in penetration depth? What surface treatment were the samples subjected to prior to in situ XRD examination?

It is my understanding that the Goebel reduces the equatorial divergence while the soller slit does the same for the axial divergence. Right?

https://www.flickr.com/photos/85210325@N04/10515372183/in/set-72157645018820696

Claudio Ferrari’s answer is the correct one! You do not have problems with the equipment.

I think Mathias Grube  detected the soller slit issue right away. Lots of good guesses with very little to go on. One real time image of the 2D incident beam would have spoken volumes :-)

Hi, Petru,

Excuse for my concise previous message. The broad peak at 2Theta approx 56 deg is from 311 Si, and it is normal to be broad because it is a tail of the peak (wrong omega and probable wrong phi). To have a sharp peak you have to determine the correct phi and omega. Besides crystal structure, omega depends also on the off-cut angle of the wafer (usually < 0.4 deg) – whose observed value depends also on phi.

But I don’t understand that large hump around 52 deg.....

Hi Petru!

we have two similar system ( D8 and D8 advance).  gone through all the suggestion,

well please do the following to confirm the problem point and its rectification:

1. First choose a standard sample (note down the thickness) in solid form not powder ( not a single crystal at first trial), select the lowest divergence slit 1/2 mm.

2. choose the intense peak of the sample (let the peak at 2theta= 30 deg). Take a diffraction pattern by aligning the z-axis ( note down the position say 10 cms).

3. Increase the z-axis very little, and take another scan, continue the same procedure for  5/ 6 points.

4. Similarly, back to the original Z-axis position ( say 10 cms), and take the scan decreasing the height (z-axis) and select 5/6 points.

5. from the above scan find the peak produce highest intensity  (note down the Z-axis position say 10.2 cms).

6. Similarly, omega and phi scan at the new z-axis position (say 10.2 cms) and compare the intensity to get maximum vale.

7. This way you can find the fault, after that you can try with single crystal with exactly same thickness, since a micron deviation in thickness may shift the peak to few degree.

ok

Thank you for your answers.

I solved the problem. As I told you the soller slit was completely missaligned. As soon as I start turning the screws the CPS went from 200 to 20 000 000. (direct beam). Thank you again for your useful answers and sugestions

Petru! If not proprietary, please post your "before" and "after" calibration (reference, alignment) diffractograms, so that we may all learn from your experiences. Thanx!

"As soon as I start turning the screws the CPS went from 200 to 20 000 000. (direct beam)". Did you do so while the beam was on? Do you have remote capabilities to do so? How  do you protect your detector? I presume 0D. How did you accomplish this Petru? What is the general process for such alignment of the soller slit? How do you confirm that the soller slit vanes are perpendicular to the incident "line source"  while being axially collinear using the 0D or the 1D detector? Is it just by looking for intensity maxima?

Here is the set-up we used for the Bruker at IISc Bengaluru. Please browse through and share your opinion in feed-back when convenient.

https://www.flickr.com/photos/85210325@N04/15271913058/

What  B. Mallick is discussing is the standard sample alignment process, in order to position the sample surface on the z-axis (collinear or at least coplanar). I wonder how long this process takes typically with a conventional 0D detector or even a 1D linear detector. I'm still in awe that some can accomplish such superhuman feat with a 0D Geiger counter.  Any suggestions on the time frame for such alignment procedures from the practicing 0D XRD system users?

Petru,

also check the image of focus (line?) on the fluorescent screen, realigning GI Soller may play you tricks, and hopefully you have the factory alignment data (corundum? standard measurement files) to compare peak height (for this one you will also need the periodically checked tube aging...), asymmetry and width values. What you see as a good alignment may be a very bad alignment.

Regards,

 Feri

Pay heed to what Feri writes!

X-ray Diffraction In Crystals, Imperfect Crystals and Amorphous Bodies by Andre Guinier. 1962 - Great book! Worth acquiring for your XRD collection.

(pp. 162-163) 6.3.5. "Comparison between the Photographic and Counter Methods

It is obvious that the Geiger Counter and the ionization chamber have the advantage of precision and sensitivity. They alone permit a quantitative study of scattering. However, point by point measurements in reciprocal space are lengthy, while the photographic method gives directly a picture of the scattering in a single experiment over a large surface of reciprocal space. The resolving power of the film is excellent. Thus, sharply defined scattering regions, for example on rows or on planes of reciprocal lattice, show up very clearly on photographic film but are difficult to detect with a counter.

Let us note also that the counter is "blind". In many cases inaccuracies in the setup produce stray scattering which is easy to detect on the photographic film but which can spoil a series of experiments made with a counter.

The two methods are therefore complimentary and it would not be advisable to neglect one in favor of the other. The photographic method is admirably suited to the qualitative exploration of an unknown pattern, since one can then find totally unexpected phenomena. The counter is necessary for quantitative measurements on a pattern which is already known qualitatively."

This was printed in 1962. This has to be considered in light of the present day 2D detectors that combine the benefits of the counter & the film in one. These writings indicate some causes for the present day inertia of moving from the 0D to the modern 2D detectors. The spatial "blindness" of the 0D scintillation counter/detector is the principal reason even experienced experts using XRD are ambivalent about the 0D XRD data/results.

Now, I'm going to confess :-) I need your help interpreting my 2D XRD alignment/calibration data with our Bruker D8 Bragg-Brentano focusing geometry/opticshttps://www.flickr.com/photos/85210325@N04/15271916978/. The zero off-set of the "Main Beam" (Incident Beam https://www.flickr.com/photos/85210325@N04/15336978941/) was not identical to the relative shift of the strongest peaks for 

CORUNDUM-https://www.flickr.com/photos/85210325@N04/15418209755/

alumina and

Si-https://www.flickr.com/photos/85210325@N04/15340063112/

powder standards. I think it would have to be sample surface displacement from the rocking axis. What say you?