I think its a reasonable way to do so, but you should keep in mind that if the sample height is not correct and you are working with a divergent beam (without Goebel-mirror), then the angular scale cannot simply be corrected by adding/subtracting an offset - you will observe angular variations within the entire diffractogram!

The thickness of the sample would distort the Ewald sphere into a spherical surface with some annular thickness to it. Is this what you mean Dirk?

I don't think the Rigaku MiniFlex (@ SIT) was equiped with a Goebel-mirror for these obervations.

Well, this what I meant!

Dirk! How would the Goebel-mirror change the outcome & why? Thanks!

Well, you have an exactly parallel beam, thus if the sample height is not correct, that does not affect the geometry of your experiment - incident as well as exit angles do not change. This is different in a parafocusing Bragg-Brentano geometry with divergent beams. If the sample is not adjusted correctly, say it is adjusted to high, then the incident agles are smaller, and the exit angles as well. See the sketch in the attached link, http://www.gly.uga.edu/Schroeder/geol6550/XRD.html

Hope this helps, in any case the mirror also gives you more flux ...

Thanks for the link Dirk!

You're welcome. There are so many beautiful and carefully maintained www-pages on X-ray diffraction and the practical problems related to that. Maybe one should start making a collection of those and post them somewhere in this forum. That would be a big deal especially for beginners ...

Why don't we start right here, Dirk? Put some up please. I'll help.

How do you want to proceed? I attach a list that I have compiled also for our students and educational purposes. Do not expect the list to be complete, I just put in the links that I personally am using ... So feel free to add your stuff! CU, Dirk

Awesome information Dirk! We all appreciate your contribution. Thanks!

Please post this as a new discussion or a "Poll" query on the following LinkedIn group when convenient: ("X-ray Diffraction Imaging for Materials Microstructural QC")

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You are all pre-approved to join and post!

Certainly post this question and others like it on the following LinkedIn Group post if possible:

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2. X-Ray Diffraction and Scattering Techniques

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If any of you are involved with materials or X-ray Diffraction, then here are some tools to help improve both the quality and quantity of your publications:

Come join us and share in the wealth of knowledge. Free Webinar, July 12 at 11am EST on X-ray Diffraction Techniques in Transmission Geometry

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Stats as of 01-25-2014 0515 hrs - 1 / 0 · 15 Answers · 412 Views

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

BTW the off-set in the "Al holder" peaks indicates an "instrument back-lash" as well, doesn't it? This makes the use of "internal standards" even more critical, doesn't it?

You have XRD pattern from your specimen on the aluminum sample holder. And you need to calculate zero shift and/or sample displacement for correction of peak positions on XRD pattern using aluminum peaks obtained from sample holder. And you perform it. Is it correct understanding of your situation? If this is true, I don't think that it is a good way. But the simplest way to check correctness of this approach-it is use of XRD pattern obtained from one more standard material (with well-known unit cell parameters) on your Al sample holder

Vladimir! That is right in order to get the correct absolute values. Standard powder such as universally accepted LaB6 powder would be efficacious. However, since the polycrystalline Aluminum sample holder is always invariant (including sampling area/voxel) hence its XRD signal may be used to calibrate for both "back-lash" and "sample displacement" w.r.t. diffractometer axis. Both system generated aberrations. Correct?

P.S. I'll try to break into smaller sentences.

Would you folks be open to a Google Hangout so that one of the experts like Dirk could walk us through some of the resources that are freely available for XRD analyses on the Internet! We could always send over some X's & O's to the good Samaritan! In XRD the data acquisition may take minutes to hours, but the analyses may take considerably longer and would require a lot of diligence for certitude & precision.

Please can you describe on which way the diffraction peaks (maximums) are shifted from standard value (linear, exponential eq.) or just for some constant value? Does you have installed sample spinner?

The misalignment of the sample surface may occur due to:

1. Sample thickness

2. Sample surface warp

Correct, but you go much more for example:

3. Particle size into used sample influence on systematic disappearance some diffraction maximums

4. systematic errors which arise from geometry and there you have a lot parameters ( such as distance detector sample, synchronization collecting diffraction maximums, optics... )

5. Presence of parasitic radiation into your beam! Presence another wavelength into main beam!

6. Misalignment of focus of X-Ray

7. Chemical composition of your sample can increase a lot your background especially if they consist some elements such as Fe, and according to the absorption factor of all elements (chemical composition) determine and of course the thickness determine the penetration of X-Ray radiation.

I hope so that i help you. If you have more question please don't hesitate to ask.

standard which you can use for calibration is Agbeh, LaB6, NaCl pure be you carefull that they have to be fresh Agbeh and LaB6 (photo sensitive) and NaCl it shold be dry and PURE, and if you wish to correct for intensity of X-Ray you can use glassy carbon.

Thanks Dražan! Your observations are an excellent summary in general. The data we are discussing here is from conventional diffractograms using a 0D point counter system. Items 3,4,5,6,7 should not shift the relative positions of the XRD Signal peaks from the "invariant" poly-crystalline Al holder. Therefore, the Al sample holder would serve as excellent "standard" in the absence of an ideal "internal" standard. This method of recording the reciprocal space does not involve "spinning the sample" but does use the Theta-2Theta coupled mode. The Debye-Scherrer Arc is fairly continuous in comparison to slit size and sampling size. All signal entering the detector slit is integrated into one relative intensity cps for each increment of Theta-2Theta. I hope I didn't confuse much.

http://www.flickr.com/photos/85210325@N04/10888339173/

Dražan! I'd also suggest you consider reviewing this real time YouTube video from the BNL Synchrotrotron Beam Line X14A of LaB6 standard powder showing the effects of "spinning" the sample on the 2D diffractogram. Real time Debye-Scherrer camera frame by frame! You'll see live examples of item numbers 1 to 7 from your earlier excellent summary! There are other interesting data sets in the play list as well. Your feedback with intellectual honesty would help us improve a lot!

[email protected]

http://www.youtube.com/watch?v=IU0m4yI7D-k&list=PL7032E2DAF1F3941F

What does the diffractogram from "Glassy Carbon" look like? Please post it when available at your earliest convenience.

Here is one pattern of glassy carbon obtained at the Austrian SAXS beamline at the Sincrotorne Trieste Elettra. Energy used for this measurng was 8.0keV

Fit2D

Original file, gc is usually has been used for detection of active part of detector and for correction of intensity from relative value on the absolute value.

Ravi, your polycrystalline Aluminum sample holder is always invariant, but your material is not always the constant. What thickness of layer that you study? Is 200mk? Is 500mk? X-rays penetration depth, which for a given wavelength is a function of the mass absorption factor and the density of the crystalline phases, is not constant. Shift of Al peaks will depend on properties of a studied material. I think that you at all won't see aluminum peaks if your sample is FeOOH, for example. And certainly it won't be essential for organic materials

Remember! Take a NIST standard and chek the goniometer and optics alignment, systematic errors, geometry abberations ;)

Dražan! "Agbeh" What is this?

Vladimir! Sure, the penetration depth is an issue. However, in this case despite the sample thickness the sample holder signal was "loud and clear". Meaning, the incident beam consistently penetrated the sample into the sample holder to produce the Aluminum diffraction pattern. We are not using the changes in the relative intensity but just the peak positions to correct any "offset".

Vladimir! "Shift of Al peaks will depend on properties of a studied material". The sample holder Al peaks will be independent of the sample mounted on it if the beam is penetrating the sample consistently. Yes? Bare in mind that in this case the Al sample holder could be essentially considered both an "internal" as well as an "external" standard since the incident beam is penetrating sufficiently into the sample holder in each case. The sample thickness above the Al sample holder should have no affect on the XRD peak positions from the Al sample holder. Yes?

Vladimir! I'm unfamiliar with your nomenclature "Is 200mk? Is 500mk?". Please clarify dimensions used.

Ferenc! "the goniometer and optics alignment, systematic errors, geometry aberrations", should be invariant sample to sample since no changes were made sample to sample on the same diffractometer other than switching the samples. The sample holder was always the same in each case. BTW I do agree about using a "NIST standard and chek".

The Al foil sample was about 0.2mm thick while the Nitrile rubber samples were 0.5 to 1mm thick. The powder samples were picked up on a scotch tape from the container without pressing such powder into any "crevice" on the sample holder. The powders were mounted with the scotch tape and thus evidencing the XRD signals from the scotch tape as well. The powder sample thickness was approximately

Silver behenate (AgBeh) is standard for calibration scatering curve in the small angle scattering range

Thanks Dražan! Would you or anyone else please post a diffractogram for such a standard? I think I found it.

https://www.google.com/search?q=silver+behenate&tbm=isch&tbo=u&source=univ&sa=X&ei=0AnlUqrQOuvKsQTrzoHQAQ&sqi=2&ved=0CDAQsAQ&biw=1366&bih=651

Note Ravi.

The type of material used and its related property is necessary.

Adeola! Certainly for the overall analysis. But, not to consider the XRD signal from the sample holder as invariant. That signal will remain despite the change in sample characteristics provided the incident beam penetrates the sample into the sample holder. http://www.flickr.com/photos/85210325@N04/8434970459/in/photostream Please review the data from various samples with the same Al sample holder on the Rigaku MiniFlex diffractometer. The XRD pattern of the sample holder in each case is invariant. Note the example below where we've used the 0.2mm Aluminum foil with "preferred orientation as the calibration standard for a 2mm thick composite sample containing crystalline and amorphous content, RDX, CAB, Al etc. 2D (transmission Laue) & 1D (reflection geometry) diffractograms are included.

http://www.flickr.com/photos/85210325@N04/7988760159/in/set-72157632728981912

Relying on a pattern from a substrate holder would be a last resource in my mind, with internal known pattern preferred but obviously seldom available, and a substrate pattern (quite obvious choice for thin films on silicon or other crystalline substrates). It depends a lot on the sample geometry and thickness, in particular.

Adam! You make an excellent point. It is also an excellent segway into the more philosophical issue of using "known standards" in XRD. I do relate to the use of established scientific XRD standards such as the ones recommended by NIST. But, I do want to note the fact that each material has a signature XRD signal unique not only for that material but depending of the spatial resolution and angular resolution available, it is unique to each sample and each crystal. This is an interesting premise because it means that any material could be used as a reference standard provided it is available to use unaltered for each observation for various samples. We are of course assuming no other changes occur between individual separate samples in terms of the experimental set-up. In general I agree that the sample holder should be the "last resort" as a calibration standard. However, our "powder" data indicates the effectiveness of such use. Imagine if the Braggs had to wait for a NIST standard LaB6 powder to continue their elegant XRD observations. They could have been denied the Nobel Prize?

I'll illustrate and discuss the effective use of non-standard calibrants in XRD from our practical observations. One of my favorite lab standards (besides the Aluminum sample holder) is the ubiquitous Aluminum foil. Aluminum foil had multifold advantages in our case. We've effectively used it as an invariant standard for all of our transmission Laue observations (2D diffractograms). Al foil doubles up as an excellent gradual X-ray beam attenuator as well. Its indispensible versatility in the XRD lab has been a boon to us. To me, this is the classic "lemons to lemonade" paradigm.

I'll also share the use of theoretically computed Bragg profiles and observed XRD Bragg profiles for mono-crystalline GaAs (standard sample) in making relative comparisons between diverse mono-crystalline samples (substrates and epi's) on the same or similar diffractometer. Case in point, we've compared results from two different Panalytical diffractometers for the same sample and observed identical results. Please watch the attached YouTube video for more details. All the original XRD data for each sample is available for review on YouTube for your convenience. http://www.youtube.com/watch?v=9SHH2GJ8IYE&list=PL7032E2DAF1F3941F

Bottom Line: Any material available with unaltered Nano structure may serve as the standard for comparative evaluation. Such a standard may be calibrated with a more "generally accepted standard" sample (such as the LaB6 standard) at any time before, during or after the XRD observations. Hence the justification for the use of the Aluminum sample holder in our case for the Rigaku Miniflex data posted earlier.

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

This may seem off topic for now but is relevant.

For those that have trouble calling a "diffractogram" a "spectrum": What about Bragg's X-ray spectrometer? Please remember even after "monochromation" there is always a spectrum of wavelengths in the incident beam ("instrument profile"). Only a synchrotron may yield a "near delta function" :-)

Honoring the two Braggs: the first X-ray crystal structure and the first X-ray spectrometer http://www.tandfonline.com/doi/pdf/10.1080/0889311X.2013.797410

http://www.tandfonline.com/doi/pdf/10.1080/0889311X.2013.797410