Talk:Electron diffraction

Complete overhaul needed

This article needs to be reworked quite a bit. Not only is it a stub, but some of the statements made are simply wrong. For example: "The technique is only used on crystal samples..." (no, it is also used for amorphous solids and gas molecules) and "The electrons are scattered by interaction with the positively charged atomic nuclei." (no, the electrons are scattered by both the nuclei and electrons surrounding the atom core.)

Perhaps we should try to outline a new article? A first draft could be something like this:

• Section: Wave-nature of electrons, link to article on interference of waves, link to article on general diffraction. Formula for wavelength of electrons as function of accelerating voltage. How are electrons scattered? Differences and similarities with photons (X-ray) and neutrons.

• Section: how is electron diffraction used in crystal structure determination? In studies of amorphous solids? In studies of gas molecules? An alternative would be to rewrite the electron crystallography article (probably better, and should probably be done anyway).

• Section: Geometry of electron diffraction in transmission

• Section: Geometry of electron diffraction in backscattering

• Section: Geometry of gas-electron diffraction

My experience is almost exclusively with electron diffraction in TEM and I'm going to need some help with the structuring and writing of this article!

oysteinp

First sketch

(October 19 2005 (oysteinp), modified October 20 (oysteinp), October 23 (oysteinp))

Could this work as a start?

Electron diffraction is a technique used to study matter by firing electrons at a sample and observing the resulting interference pattern. This phenomenon occurs due to the wave-particle duality, which states that a particle of matter (in this case the incident electron) just as well can be described as a wave. The electron is then diffracted in a similar fashion as classical waves such as sound or waves in water. This technique is similar to X-ray diffraction and neutron diffraction.

Electron diffraction is most frequently used in solid state physics and chemistry to study the crystal structure of solids. The periodic structure of a crystalline solid acts as a diffraction grating, scattering the electrons in a predictable manner. Working back from the observed diffraction pattern, it may be possible to deduce the crystal structure giving rise to that particular pattern. However, the technique is limited by the phase problem.

Apart from the study of crystals, electron diffraction is also a useful technique to study the short range order of amorphous solids, and the geometry of gaseous molecules.

Theory The wavelength of an electron is given by the de Broglie equation

$\lambda ={\frac {h}{p}}$

Here $h$ is Planck's constant, $p$ the momentum of the electron and $m_{0}$ its mass. The electrons are accelerated in an electric potential $U$ to the desired velocity:

$v={\sqrt {\frac {2eU}{m_{0}}}}$

The electron wavelength is then given by:

$\lambda ={\frac {h}{p}}={\frac {h}{m_{0}v}}={\frac {h}{\sqrt {2m_{0}eU}}}$

However, in an electron microscope, the accelerating potential is usually several thousand volts causing the electron to travel at an appreciable fraction of the speed of light. An SEM may typically operate at an accelerating potential of 10.000 volts (10 kV) giving an electron velocity approximately 20% of the speed of light, while a typical TEM can operate at 200 kV raising the electron velocity to 70% the speed of light. We therefore need to take relativistic effects into account. It can be shown that the electron wavelength is then modified according to:

$\lambda ={\frac {h}{\sqrt {2m_{0}eU}}}{\frac {1}{\sqrt {1+{\frac {eU}{2mc^{2}}}}}}$

We recognize the first term in this final expression as the non-relativistc expression derived above, while the last term is a relativistic correction factor. The wavelength of the electrons in a 10 kV SEM is then 12.3 x 10^-12 m (12.3 pm) while in a 200 kV TEM the wavelength is 2.5 pm. In comparison the wavelength of X-rays usually used in X-ray diffraction is in the order of 100 pm (Cu kα: λ=154 pm).

• How are electrons scattered?
• Differences and similarities with photons (X-ray) and neutrons.

Electron diffraction in the TEM

Sketch of the electron beam-path in a TEM.

Electron diffraction of solids is usually performed in a Transmission Electron Microscope (TEM) where the electrons pass through a thin film of the material to be studied. The resulting diffraction pattern is then observed on a fluorescent screen or recorded on photographic film or a CCD camera. In the TEM, electron diffraction can be combined with a range of other techniques such as chemical analysis of the sample composition through energy-dispersive X-ray spectroscopy, direct imaging of the sample, including high resolution imaging of the crystal lattice, electron energy loss spectroscopy, and electron holography.

Geometry of electron diffraction in backscattering

Geometry of gas-electron diffraction

TEM-sentric

(23 October 2005, oysteinp) The article sketch I've posted above is becoming a little TEM-sentric. I'm sure there are lots of people out there that could add info om other forms of electron diffraction!

Why don't you just edit the article directly? You seem to know what you are talking about, don't be timid. linas 06:58, 22 November 2005 (UTC)

Well, ok. I just thought it would be a good idea to discuss the content of the article :) But anyway: I've updated parts of the article. I'll work some more on it later. O. Prytz 21:09, 22 November 2005 (UTC)

For highly contentious articles, where many people are arguing over many things, that would be a very good, and polite, thing to do. This article, by contrast, suffers from neglect: no one is bothering much to edit it, and so there won't be much of a discussion, either. As long as you are ot adding patent non-sense, you'll have free reign. linas 00:12, 23 November 2005 (UTC)

I've written a bit more in the section on electron interation with matter, it's mostly a comparison of the different forms of interaction applicable to electrons vs. neutrons vs. X-rays. Could anyone have a look at this? I'm a bit uncertain about the details of this section and it would be good if someone could check the validity of the statements. O. Prytz 20:44, 6 December 2005 (UTC)

Done. Only the strong interaction counted for the nuclear force. I simplified the x-ray sentance. linas 04:55, 7 December 2005 (UTC)

I've added a section on electron diffraction in a TEM, a couple of figures and a reference. O. Prytz 14:45, 18 December 2005 (UTC)

New section

I've added a new section on the intensity of diffracted electron beams. It's not quite done yet. But the real question is really: how detailed should a Wikipedia article be? I mean: you could write a textbook if you like, but is that really appropriate?O. Prytz 13:05, 21 December 2005 (UTC)

I've fleshed out the Electron diffraction in TEM section a bit with a discussion of the benefits of this technique. I'll add a section on limitations later. Once againg I'm worried that the article may become a little too detailed and focused on TEM. Furthermore, maybe some of the content should be moved to the electron crystallography article (which really needs some work). O. Prytz 10:13, 31 December 2005 (UTC)

Done for now

Ok, I finished the section on limitations, but I'm afraid it's prettey POV so please have a look and rewrite/delete anything not belonging in an encyclopedia. I'll be adding some refrences to the article sooner or later... I'm still a bit worried that the article gives undue weight to electron diffraction in TEM. I might eventually move some of the content to electron crystallography which needs a bit of work. O. Prytz 19:20, 2 January 2006 (UTC)

Thanks! For the most part, it looks pretty good. You might also consider starting a new article electron diffraction in TEM, maybe. Or maybe nt. Eithre way, thanks. linas 21:09, 3 January 2006 (UTC)

Hm...that might be a good idea, although I think I'll wait until I've had a go at electron crystallography. O. Prytz 20:31, 4 January 2006 (UTC)

TEM centric

It's TEM centric because electron diffraction can be done on most any TEM, while it's not often done on an SEM. Why is the wavelength of the electron in an SEM so prominent and first when electron diffraction in an SEM is hardly touched upon? The order should be changed to reflect that the article includes extensive information about TEM electron diffraction, not SEM. --Blechnic (talk) 06:44, 28 May 2008 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Electron diffraction/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Seems like an okay article, but it needs more references first of all Snailwalker | talk 14:13, 19 October 2006 (UTC)

Last edited at 14:13, 19 October 2006 (UTC). Substituted at 14:19, 29 April 2016 (UTC)

External links modified (January 2018)

Hello fellow Wikipedians,

I have just modified one external link on Electron diffraction. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://web.archive.org/web/20070728014559/http://rcl.physik.uni-kl.de/ to http://rcl.physik.uni-kl.de/

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 03:13, 22 January 2018 (UTC)

Article rating after substantial transform

Dear fellow Wikipedians,

the article has undergone a substantial transform in recent weeks (before and after) and I hope its rating became out-dated. If I understand it well, the rating can only be changed manually. If you agree the B is out-dated, could you please help me with changing it appropriately?

Similarly, there is an article about Selected area diffraction which I hope is not a Stub any more and another one about CrysTBox which has not been rated at all.

Thank you very much for your help.

Klingm01 (talk) 18:07, 7 March 2022 (UTC)

This article needs major work

This article, at least in it's current form, contains major errors of science. There are also some grammatical issues, although these are less severe Ldm1954 (talk) 11:18, 18 January 2023 (UTC)

Please fix it and include references for your additions / corrections. Regards, Ariconte (talk) 20:27, 18 January 2023 (UTC)

Thank you for your willingness to improve the article. However, deleting the whole Theory section (incl. all images, tables and formulas) is definitely not the best way. I'm not saying the section is perfect, but formulas and tables taken from the literature (see the references) are definitely not scientifically wrong neither are images showing the relation between spot and ring diffraction or what Kikuchi lines are. I hope that gradual edits (like those you have yourself made in this very section before deleting it) are much better way to improve the article. --Klingm01 (talk) 12:22, 4 February 2023 (UTC)

As someone who has taught the topic for decades, and extensively published I will tell you the section is awful, and misleading:

1. The non-relativistic wavelength form is never used.

2. The relativistic form is incorrect, as an effective mass is used to cancel some terms (see Hirsch et al or Peng, Dudarev & Whelan).

3. The statements/equations about kinematical theory are completely wrong -- there is a |sin(pi*t*sz)/(pi*sz)|**2 missing.

4. The "effects of crystallinity" is misleading, for instance double diffraction is ignored

5. As written the Kikuchi line section does not belong in this section. To do the theory properly Bloch waves have to be introduced first, which would be a large digression.

6 The gas phase section is also not theory.

While I understand that you want to give people a simple explanation so they can use simple codes, that takes knowledge backwards. The whole theory section must be removed. Electron diffraction is not simple.

Ldm1954 (talk) 11:22, 7 February 2023 (UTC)

References are soft

The references are very weak, and do not include the major physics sources, for instance:

1. Hirsch et al, the yellow bible.

2. Cowley, diffraction physics.

3. Peng, Dudarev and Whelan -- for current dynamical

4. Zuo and Spence on microdiffraction

The ones mentioned are decent introductions, but do not go close to far enough. Ldm1954 (talk) 11:32, 7 February 2023 (UTC)

Unfortunately, I can't see any of these references in the article. Add them to the article instead of criticizing or vandalizing existing references. Klingm01 (talk) 14:39, 7 February 2023 (UTC)

Incomplete coverage

There needs to be some sections on LEED, RHEED, PED, 4D-STEM. The current version is too biased towards simple SAED.

It also does not include important artifacts/effects such as positional errors in SAED, projector lens distortions, dynamically allowed spots, HOLZ, GM lines...(an incomplete list). Ldm1954 (talk) 11:38, 7 February 2023 (UTC)

Please, stop vandalizing the article

Lets's be minimalistic. Dear Ldm1954, feel free to continue with personal offenses and humiliations, feel free to improve the article, but please stop vandalizing it. After your edits, there are errors, empty sections, references to removed images, not mentioning the content. Klingm01 (talk) 14:58, 7 February 2023 (UTC)

The prior version would fail any decent TEM class at a strong university. Sorry, but that is reality. It is not "personal offenses", this is scientific rigor.

The current version is adequate, although I would still only give it a B-. I have to go and teach TEM, and will add more references later and further clarifications -- they are needed. Ldm1954 (talk) 16:06, 7 February 2023 (UTC)

Ldm1954, do stop vandalizing the article

Dear Ldm1954, your expertise is most welcome. Instead of using it to disparage others and their contributions, please use it to improve the article. As mentioned before, the article is not necessarily perfect, but this does not mean, you can freely remove its substantial parts without providing better alternative.

Repeated removal of substantial content and claims of incorrect information

Above, you claim the "relativistic form is incorrect" and you say

"While I understand that you want to give people a simple explanation so they can use simple codes, that takes knowledge backwards. The whole theory section must be removed. Electron diffraction is not simple."

You have removed all the formulas claiming they were wrong and too simple. What have you left there instead? Nothing. Your repeated removal of Theory section leaves an impression that there is no theory behind the diffraction. This is what "takes knowledge backwards".

Moreover, you claim the relativistic wavelength formula and/or table to be incorrect. I have just checked the formula in the article and it equals to the one stated in Prof. Kirkland's book (see the references). If there is a mistake, please fix it in the article and inform Prof. Kirkland accordingly. If there is a mistake in the wavelength table, please tell us where. Carter&Williams, Karlík, de Graef - I have just checked their books and they all state exactly the same values you have deleted for being incorrect.

Article structure

The structure of the article had its purpose:

1. History
2. Theory - Non-relativistic, relativistic, material structure (singe/poly-crystal) etc.
3. Applications - TEM (SAED, CBED etc.), SEM, Gases

This structure guided the reader from the History (from the first experiments up to de Brogile), then via the Theory (the reader could read the de Brogie's formula mentioned in the history, see its place in theory, via non-relativistic to the relativistic etc.), showing the impact of material structure on the diffractogram (single- vs. poly-crystal). The the Applications decribed TEM (it's importance from ED point, the beam and image formation, and individual experimental techniquies like SAED or CBED etc.), followed by SEM and gases.

As you know, the strengths and traps of the diffraction imaging originate from the fact, that the image is formed by so many factors at once - if we stay very simple, it's material structure, beam parameters and detectors. Please note here, that the original structure kept those factors separated instead of mixing them all together. This is crucial for understanding the influence of the individual aspects on the resulting diffraction.

Please note also, that the structure allowed the article to be read in whole (with a continuous flow and gradual information develpment) as well as in parts (individual subsections as self-supporting as possible).

After you "rationalized" the structure we have:

1. History
2. Types of electron diffraction

In the giant, unstructured section called Types of electron diffraction, you put together different instrument, phenomena or techniques with no respect to their functional or causal relations. At the same level in one single section, you mix together

• experimental instruments (TEM, SEM, RHEED)
• experimental techniques (CBED, 4D STEM, Precession etc.)
• material structure (singe- vs. poly-crystalline samples)
• general information specific to TEM (formation of image in TEM)
• theory (double diffraction)
• diffractogram features (Kikuchi lines)

This looks as if the Scanning electron microscope shared the category and level with Kikuchi lines. This is extremely confusing. Of course, experts can orient themselves in this chaos, but beginners or cross-disciplinary people will be lost and confused. And this is encyclopedia - it should be readable for a broader audience.

Summary

These are just the major areas of arguments qualifying your activities as vandalism. I am not mentioning particularities like that you should prepare your edits in your sandbox instead of continuously editing the article visited by the readers meanwhile or that the non-realistic wavelength, which is mentioned in all relevant books, is relevant here, it allows to bridge the History and Theory and it's extent is proportional.

Please, do not repeat your vandalizing activity. As mentioned repeatedly, you are welcome to improve the articles. Try to focus on smaller, gradual changes. This does not mean, however, removing each Theory subsection individually (12:23, 7 February 2023‎ and later) instead of removing it at once (19:13, 2 February 2023). It means correcting particular mistakes as you spot them and can prove them. Before more substantial edits, feel free to contact the original authors or discuss them here on the talk page.

Your knowledge is needed, but use it constructively.

Klingm01 (talk) 12:56, 8 February 2023 (UTC)