"relaxation phenomenon induced by the high energy" in the tube target or the sample? How do you see this affecting the XRD data?

Aek! Don't worry, you are among friends. The point behind the question is that the fear of loss of alignment is so severe that folks are immobilized from trying new and innovative optics, geometry & detectors on existing universal XRD equipment. The inability to visualize the X-ray beam and optics in real time is a dramatic "handicap" that experimentalists have lived with for nearly a century. The past 3 decades at least, without cause. Been there done that!

Hatem! I guess this is one of the dreads. Repeating an experiment 10 times. I've often used and recommend using internal/external calibration standards. With a standard, appropriate corrections can be made to account for instrumental aberrations and any other systematic changes including equipment "drift" as well as potential "relaxation phenomenon induced by the high energy". In my case due to lack of in-house X-ray source, we have to get as much data in as little time. Usually minutes at a time at most few hours. Virtually about 20 minutes of real time XRD video data from 5 samples has taken me 2 years to thoroughly analyze in reciprocal space.

All of the above, certainly, but also:

5. Continuity/repeatability of results. If I make a dozen measurements on a sample heat treated for different lengths of time, for example, I'm more interested in the differences than the absolute high quality of any one dataset. I want to know that nothing else has changed between XRD runs, and that includes changes to the alignment of the diffractometer - even if it's designed to give me a better count rate!

Philip! "I want to know that nothing else has changed between XRD runs". Precisely!

When I am confronted with this paradigm, I think of the good old Ronald Regan malapropism "Doviyay no proviyay". This should correctly have been "Доверяй, но проверяй" (Doveryay, no proveryay) meaning "trust but verify". Therefore, no matter who says what about their diffractometer, I always verify using a known standard and record the incident beam characteristics for each individual run prior to each individual diffractogram when possible. I record the incident beam prior to each sample at the least. This accommodates for any variance in alignment etc. from diffractometer to diffractometer or day to day. Here for example is an array of incident beams from various diffractometers at various locations. This procedure of recording the incident beam characteristics is critical for consistent interpretation of Bragg XRD Micrographs.

1. BNL Panalytical X'Pert incident beam:

http://www.flickr.com/photos/85210325@N04/8646857294/in/set-72157635534175171

2. AFRL Panalytical MRD incident beam:

http://www.flickr.com/photos/85210325@N04/8646862334/in/set-72157635534175171

http://www.flickr.com/photos/85210325@N04/9531061382/in/set-72157635534175171

3. SMIF Panalytical MRD incident beam:

http://www.flickr.com/photos/85210325@N04/9248173496/in/set-72157635534175171

4. All incident beams compared with that from a BEDE diffractometer (NC A&T):

http://www.flickr.com/photos/85210325@N04/9447771903/in/set-72157635534175171

My hypothesis: "Fear of the unknown", in my opinion, is the real cause of such consternation generally! As it was for me prior to the "revelation" during the 1980's @ RU & JHU. My challenge is to substantiate or nullify this hypothesis. Practically, it becomes a "piece of cake" once you start seeing the "unseen" X-ray images in real time, safely, quantitatively & remotely!

http://www.flickr.com/photos/85210325@N04/9248173496/in/set-72157635534175171

I just shared this question with nearly 170 on my contact list. Let us see the statisics after this move.

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I'm in agreement with the above. The last thing required if you need to perform several runs over a period of time is the fact someone else can come along and 'change' something fundamental with the set-up.

At least if there is an error in the alignment set-up, the same will occur in all sets of results, although this is unwanted, at least not all of the data collected needs to be discarded.

In simple terms, I believe when you are granted time on a piece of equipment of such accuracy, one believes one actually 'owns' the machine for that length of time and does not want other people interfering with 'their machine and their time' - just as the next person wouldn't want the same interruption.

I believe some scientists are far more considerate than others to how they leave equipment after running an experiment; as I have often found when working on larger testing diffraction facilities such as ISIS and ILL.

I am not sure about what I understood from the overall scope of the question, but I think that the accuracy and the repeatability of the runs is affected by the relaxation phenomenon induced by the high energy of the X-rays beam, while going from one run to another. Please note that my background on this topic is very modest.

Any X-ray diffraction run should be the same if it is repeated 10 times under the same conditions and circumstances.

"relaxation phenomenon induced by the high energy" in the tube target or the sample? How do you see this affecting the XRD data?

Aek! Don't worry, you are among friends. The point behind the question is that the fear of loss of alignment is so severe that folks are immobilized from trying new and innovative optics, geometry & detectors on existing universal XRD equipment. The inability to visualize the X-ray beam and optics in real time is a dramatic "handicap" that experimentalists have lived with for nearly a century. The past 3 decades at least, without cause. Been there done that!

Hatem! I guess this is one of the dreads. Repeating an experiment 10 times. I've often used and recommend using internal/external calibration standards. With a standard, appropriate corrections can be made to account for instrumental aberrations and any other systematic changes including equipment "drift" as well as potential "relaxation phenomenon induced by the high energy". In my case due to lack of in-house X-ray source, we have to get as much data in as little time. Usually minutes at a time at most few hours. Virtually about 20 minutes of real time XRD video data from 5 samples has taken me 2 years to thoroughly analyze in reciprocal space.

Lack of training is subjective, if someone is trained to run the measurements, than (re)aligning of a diffractometer is out of question (the service will do it, however...). However, any user could be familiar with the simple steps of a goniometer set-up and alignment... On the other hand, switching between optics and geometries of laboratory diffractometers (as I do), although is not always complicated, I prefer to avoid it as much as possible. I do it, whenever it's necessary or "worth the work" but not as amusement for boring afternoons. As long as measurements can be carried out effectively, I don't don't think one should disrupt an alignment. As regards the regular alignment verification with standards, that should be mandatory (weekly, monthly, etc.), despite the fact that most laboratory systems don't require it.

On the topic of trusting in results: if someone has has to go for xrd on a contract or favor basis they should have their own system to check the quality of results (e.g. samples with internal standards, a mixture with known composition, a third party to verify results, etc.). Otherwise trusting is the only solution.

The new powder diffractometers can effectively obtain good structural data from polycrystalline materials. The technology has improved greatly over the diffractometers used late last century and this must be added the informatics that facilitates obtaining current diffraction data. The informatization of equipment allows to obtain powder diagrams over short periods of time. However the commercialization of the equipment is not always correct. Some commercial now not know the advantages and disadvantages of the type of diffractometer sold. Most have a low level of knowledge of X-ray crystallography Some, now old, we miss the first commercial and technicians of the past. But this is the present, and the young have to try to solve it. If structural results are currently better is that this is possible.

Clearly 'Garbage in Garbage out' applies if not subject to your points 1-4 above. Powder diffraction suffers because it is nowadays fundamentally easy to measure a standard sample on a commercial diffractometer. However how many researchers consider alignment, precision, reproducibility and relevant instrumental standards with each batch of measurements?

At my (commercial) institution we employ highly trained/experienced diffraction experts (not technicians) who are tasked not to just keep the instruments running but to address these important issues. They can also advance specialist diffraction knowledge so for example we dont rely on the many assumptions of the Scherrer equation to obtain size information. A template I would ideally like to see throughout the diffraction community. Realistically that is not going to happen in most institutions and then it all comes back to education. This forum/topic is therefore a worthwhile start. Thanks Ravi!

Murder? Wow, I see Blood!!!. All of the above.

In the military, an elite soldier is taught to take his/her weapon apart and put it back together with the lights turned out. That's the expertise & familiarity we as XRD specialists need to have with our instrumentation. Real time 2D XRD imaging allows this to occur. When I have the opportunity to make measurements at any facility, it is usually quite random and I have no control over the prior condition of the equipment. So, I start from scratch. Thankfully, with real time 2D image as seen by the "detector" in any XRD instrumentation allows for dynamic verification of precision and alignment. We have experimental evidence of such claim through the XRD data obtained @ BNL & AFRL on identical Panalytical instrumentation with the same samples of 3" SiC 4H & 6H wafers.(http://www.flickr.com/photos/85210325@N04/8112360290/)

1. SiC 6H (0006) Symmetric Reflection Bragg XRD Microscopy: http://www.flickr.com/photos/85210325@N04/10019182954/

2. GaAs Standard (004) Symmetric Reflection Bragg XRD Microscopy: http://www.flickr.com/photos/85210325@N04/10502393183/

[email protected]

"Bloody Murder"! - Dramatization through a cliché, Samuel? Lol!

Maybe I pass at my trial on technical (I have known excellent) of companies that sell the equipment diffraction pattern. It was a judgment as a retired user, not active, currently lacking a clearer documentation which can be obtained from a team of X-ray diffraction There are many variants (diffractometer geometry, sample holder, differences and advantages between the different types of detectors, type of windows that should be used, with or without monochromator, revisions, time to use a standard to detect anomalies in the team ....) . Explanations are not always clear to the technical universities or institutes should check the functioning of the equipment.

What is the problem? In my opinion, the diffractometer needs a "Pope", i.e. the person who knows as to perform alignment. Certainly, it is pleasant to know that alignment of your diffractometer is ideal (the maximum intensity and the minimum errors). But we after all know that modern software allow take into account various errors in alignment. And we have the reference samples to monitor the "health" of the instrument (alignment and tube dying)

" reference samples to monitor the "health"" - I agree Vladimir! Not the "Pope" or Patriarch or Tzar or Czar, yet. Lol!

Dear Ravi, you asked a question, gave the answer on it, and practically all agreed with you. And now you speak that "Popa" isn't necessary. The diffractometer is simply a device for XRD pattern recording. But this device is more complicated and costly than ordinary watch or fountain pen. Is it pleasant for you, when other person uses your watch or fountain pen as he wants?

Vladimir! Da! Can! Yes! I meant "Pope" sarcastically as the one who approves or "figurehead". You meant more from a "resident expert or specialist". Yes? I also agree that not all should be allowed to adjust "fine alignment" unless one understands the XRD techniques well. But, all users & experimenters must verify alignment with "known standards". We have clearly established the myriad of potential challenges in data precision & interpretation of the results. I have no disagreement with you. Especially, if you do not have a 2D real time XRD imaging tool for alignment purposes at the least. This is precisely what got me in the quest for real time XRD imaging: Orienting & aligning crystals to optimize Bragg condition. Precise instrument alignment was & is critical for XRD microscopy.

I'll show you some results/simulations of conventional diffractograms using 2D data which is tantamount to most diffractograms in present use. The objective is to draw comparison in terms of SNR (Signal to Noise Ratio) & DDR (Data Dynamic Range) between the conventional 0D point counter data and the advanced 2D real time data.

5 / 0 · 18 Answers · 240 Views 01/17/2014

I'd say that "sharing" the question with my erudite contacts works well. Huge up-tick in activity in two days. Most importantly, I like the participant contents from the "wise ones" on RG.

I certainly agree that there should be one person with overall control of and responsibility for any system. I do approve of users carrying out routine alignments, but please let's make sure they're properly trained and competent first. Otherwise, it's far too easy to end up with a setup that doesn't work or - and this is perhaps worse - one which LOOKS to be giving sensible data but which is nevertheless wrong. Routine calibration against known standards!

"Standards" seems to be a consensus! I'd go further and include such a scan of the standard with each sample. Especially, when publishing for that specific diffractometer. Such addition of standard data will allow scientist to potentially confirm through their own verifications and analyses of the subject data rather than be ambivalent. Just a thought. I've not delved deeper into the logistics involved with the conventional "Jurassic" XRD equipment. I've successfully used this strategy routinely for our real time 2D XRD Microscopic observations.

Perhaps publication of scans of standard samples alongside actual results - or at least in the accompanying supplemental data - is something to be encouraged. These days, it's possible to make any amount of data available somewhere, so why not? Certainly it would help to ensure published data is repeatable.

Most data obtained by scholars are obtained from facilities which are not accessible directly.

The trained person are often missing in many facilities and semiskilled technician or project assistant are ignorant of many issues. The most prominent answer would be 4.

4. Lack of training in the awesome art & science of XRD. Like the use of internal/external standards.

This is certainly fixable! Here's a modest start: http://www.flickr.com/photos/85210325@N04/10515372183/

Real time XRD Imaging or XRD Microscopy is the ultimate "idiot proof" panacea! 3S or SSS (Simple Straightforward Solution) for all XRD ailments! [email protected]

This is a good start and definitely will try to spread the awareness as 4 th option is most common problem. And it is not just true for XRD. A common problem is when one technician leaves without training next one, next one has to learn everything from start. Many a time a Ph. D. student is placed for handling instruments instead of trained person. By the time he learns instrument, it is time for him to leave. :(

I feel RG helps here as questions can be asked to the experts.

Alright! Let's see how many of you can wrap your minds around this video. It is a sequence of images from a Bragg XRD Microscope mounted on a Panalytical X'Pert/MRD type diffractometer equipped with a 6 circle goniometer to manipulate the monocrystalline wafers. The optics included a Bartel (220) 2 Bounce beam conditioner and a soller slit to minimize axial divergence. A technique called XRD Rocking Curve Microscopy is employed to quantitatively evaluate the Nano structure at each VOXEL in real space by recording and analyzing the 3D reciprocal space for each VOXEL. There are self explanatory captions in the YouTube video. Based on interest and comments I shall elaborate further. Essentially, we are correlating deviation from ideal Bragg condition to material Nano structure directly.

The use of following methods in XRD are illustrated:

1. Quantitatively characterizing the incident beam.

2. Numerical modeling of theoretical XRD profile. Kindly provided by Dr. Wayne Lin of Bruker using the veritable LEPTOS software.

3. Comparison of Theoretical & Experimental XRD Profiles.

4. Using "known" laboratory standard samples to compare other samples.

5. Use of precise numerical BG (Back-Ground) detection methods.

6. Use of data normalization methods employing "total integrated intensity under the Bragg profile" to evaluate topographic data precisely.

7. Use of INVARIENT penetration depth to measure MBE epitaxial film thickness (through diffracting volume computations) on topologically "flat" specimen.

8. Using the substrate as the "standard" in MBE grown epitaxial films (50nm & 0.5um) to evaluate film Nano structure and thickness.

9. Correlating data from the same sample of 3" SiC 6H wafer from 2 independent Panalytical diffractometers.

10. Rapid, NDE, in situ, automated characterization of materials' Nano structure in a 2D Microscopic mode! High spatial resolution (5-80um with sub-micron capability) & high dynamic range (8-24 Bit) real time data (5-300 fps)!

We acknowledge the invaluable aid of Dr. Ivan Bozovic of BNL and Dr. Kurt Eyink/Dr. Dave Tomich of AFRL/WPAFB in acquiring the subject XRD data. For a complete viewing of all the raw data and additional validation please study this YouTube "Play List" with some choice music to compliment.http://www.youtube.com/watch?v=9SHH2GJ8IYE&list=PL7032E2DAF1F3941F

Your feed-back in the form of comments would be deeply gratifying either way as would your suggestions in guidance to improve.

[email protected]

http://www.youtube.com/watch?v=SMBHjkMWDi0

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I've just shared this with 384 contacts. Let us observe the changes.

Stats as of 09-24-14 14:41 EST - 6 / 1  ·  27 Answers  ·  481 Views 

14 followers & 12 contributors 

I have some nice recent 32um spatial resolution 2D real time XRD alignment data for a Bruker D8 Bragg-Brentano focusing optics powder diffractometer @ TATA Institute of Science (Indian Institute of Science Bengaluru). For more details be unafraid to join the discussion noted below and contribute:

https://www.linkedin.com/groupAnswers?viewQuestionAndAnswers=&discussionID=5920491640274853889&gid=2683600&goback=%2Egde_2683600_member_5919808093675360259%2Egmr_2683600%2Egde_2683600_member_5810700387807698945#commentID_null

https://www.flickr.com/photos/85210325@N04/15336978941/

Near ideal alignment quantification of the Bruker D8. Please tell me if you'd have done any different. I'll fix it for the next time!

"Grabbing the bull by the horn" or "grabbing the tiger by its tail" is kind of like staring the "main beam in its face" :-) Ever done it? https://www.flickr.com/photos/85210325@N04/15336978941/

Image of our detector AXIS142532 rendered on a Bruker system just as we had it mounted for these observations. It took us all of 5 minutes to mount, come on-line and start gathering 2D real time XRD video graphic data through USB. https://www.flickr.com/photos/85210325@N04/13620538183/in/set-72157632729013664

Bragg Brentano optics used: http://pd.chem.ucl.ac.uk/pdnn/inst1/bgbtano1.gif

A Si powder standard was then used to observe the corresponding Debye-Scherrer (D-S) Arc in real time. Here are the images from both 240mm SDD (focused) and 150mm SDD (defocused). The distinction is stark!

Image of Si (hkl) at a 240mm SDD showing distinct focused spots potentially from the relatively large particle/grain size of the Si standard powder: https://www.flickr.com/photos/85210325@N04/15340063112/

Image of Si (hkl) at a 150mm SDD showing de-focused spots, a smudged D-S arc:

https://www.flickr.com/photos/85210325@N04/15340410155/

Interesting observations to report just for this Si standard data includes:

(1). It takes us only minutes to mount and dismount our technology on most existing XRD instrumentation. But it takes weeks, months, years, decades to overcome the skepticism of the "conventionalistas"!

(2). The evidence of "preferred orientation" in the Si standard sample prepared is unmistakable.

(3). Evidence of large grain size is unequivocal.

(4). The ability of the 2D detector to distinguish the difference in focal geometry is clear.

(5). The ability to conduct rocking curve analyses with large polycrystalline composites is also evident.

(6) The angular offset (0.65 degree) of the (hkl) for the Si standard powder is inconsistent with the "zero-offset" (1.375 degree) of the incident beam. This needs to be precisely verified again to be unequivocal. The sample surface location on the diffractometer z-axis (rocking axis) needs to be reaffirmed eliminating any sample surface displacement errors. I'll go through my computations again, as well.

(7) Many more D-S arcs are faintly visible in the background of the integrated 2D XRD images especially for the smaller SDD (sample to detector distance). More higher resolution observations are needed to resolve!

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I've increased the number of topics to 13. Here is a related RG discussion:

https://www.researchgate.net/post/Sample_surface_positioning_collinear_to_the_diffractometer_axis_is_critical_for_precision_in_XRD_What_is_the_conventional_alignment_procedure