Editing Electron diffraction (section)

=== Electron microscopes and early electron diffraction ===
{{See also|Transmission Electron Microscopy#History|label 1=History of transmission electron microscopy}}

In order to have a practical microscope or diffractometer, just having an electron beam was not enough, it needed to be controlled. Many developments laid the groundwork of [[electron optics]]; see the paper by Chester J. Calbick for an overview of the early work.<ref>{{Cite journal |last=Calbick |first=C. J. |date=1944 |title=Historical Background of Electron Optics |url=http://aip.scitation.org/doi/10.1063/1.1707371 |journal=Journal of Applied Physics |language=en |volume=15 |issue=10 |pages=685–690 |doi=10.1063/1.1707371 |bibcode=1944JAP....15..685C |issn=0021-8979|url-access=subscription }}</ref> One significant step was the work of [[Heinrich Hertz]] in 1883<ref>{{Citation |last=Hertz |first=Heinrich |title=Introduction to Heinrich Hertz's Miscellaneous Papers (1895) by Philipp Lenard |date=2019 |url=http://dx.doi.org/10.4324/9780429198960-4 |work=Heinrich Rudolf Hertz (1857–1894) |pages=87–88 |publisher=Routledge |doi=10.4324/9780429198960-4 |isbn=978-0-429-19896-0 |s2cid=195494352 |access-date=2023-02-24|url-access=subscription }}</ref> who made a cathode-ray tube with electrostatic and magnetic deflection, demonstrating manipulation of the direction of an electron beam. Others were focusing of electrons by an axial magnetic field by [[Emil Wiechert]] in 1899,<ref>{{Cite journal |last=Wiechert |first=E. |date=1899 |title=Experimentelle Untersuchungen über die Geschwindigkeit und die magnetische Ablenkbarkeit der Kathodenstrahlen |url=https://onlinelibrary.wiley.com/doi/10.1002/andp.18993051203 |journal=Annalen der Physik und Chemie |language=de |volume=305 |issue=12 |pages=739–766 |doi=10.1002/andp.18993051203|bibcode=1899AnP...305..739W }}</ref> improved oxide-coated cathodes which produced more electrons by [[Arthur Wehnelt]] in 1905<ref>{{Cite journal |last=Wehnelt |first=A. |date=1905 |title=X. On the discharge of negative ions by glowing metallic oxides, and allied phenomena |url=https://www.tandfonline.com/doi/full/10.1080/14786440509463347 |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |language=en |volume=10 |issue=55 |pages=80–90 |doi=10.1080/14786440509463347 |issn=1941-5982}}</ref> and the development of the electromagnetic lens in 1926 by [[Hans Busch]].<ref>{{Cite journal |last=Busch |first=H. |date=1926 |title=Berechnung der Bahn von Kathodenstrahlen im axialsymmetrischen elektromagnetischen Felde |url=https://onlinelibrary.wiley.com/doi/10.1002/andp.19263862507 |journal=Annalen der Physik |language=de |volume=386 |issue=25 |pages=974–993 |doi=10.1002/andp.19263862507|bibcode=1926AnP...386..974B |url-access=subscription }}</ref>

{{anchor|Figure 5}}[[File:Ernst Ruska Electron Microscope - Deutsches Museum - Munich-edit.jpg|Figure 5: Replica built in 1980 by Ernst Ruska of the original electron microscope, in the Deutsches Museum in Munich|thumb|alt=An images of a replica of one of the original electron microscopes which is now in a museum in Germany]]

Building an electron microscope involves combining these elements, similar to an [[optical microscope]] but with magnetic or electrostatic lenses instead of glass ones. To this day the issue of who invented the transmission electron microscope is controversial, as discussed by Thomas Mulvey<ref name=Mulvey/> and more recently by Yaping Tao.<ref>{{Cite book |last=Tao |first=Yaping |title=Proceedings of the 3rd International Conference on Contemporary Education, Social Sciences and Humanities (ICCESSH 2018) |date=2018 |publisher=Atlantis Press |isbn=978-94-6252-528-3 |series=Advances in Social Science, Education and Humanities Research |pages=1438–1441 |language=en |chapter=A Historical Investigation of the Debates on the Invention and Invention Rights of Electron Microscope |doi=10.2991/iccessh-18.2018.313 |chapter-url=https://www.atlantis-press.com/proceedings/iccessh-18/25898208 |doi-access=free}}</ref> Extensive additional information can be found in the articles by Martin Freundlich,<ref>{{Cite journal |last=Freundlich |first=Martin M. |date=1963 |title=Origin of the Electron Microscope: The history of a great invention, and of a misconception concerning the inventors, is reviewed. |url=https://www.science.org/doi/10.1126/science.142.3589.185 |journal=Science |language=en |volume=142 |issue=3589 |pages=185–188 |doi=10.1126/science.142.3589.185 |pmid=14057363 |issn=0036-8075|url-access=subscription }}</ref> [[Reinhold Rudenberg|Reinhold Rüdenberg]]<ref name="Rüdenberg">{{Citation |last=Rüdenberg |first=Reinhold |title=Origin and Background of the Invention of the Electron Microscope |date=2010 |url=http://dx.doi.org/10.1016/s1076-5670(10)60005-5 |series=Advances in Imaging and Electron Physics |volume=160 |pages=171–205 |publisher=Elsevier |doi=10.1016/s1076-5670(10)60005-5 |isbn=9780123810175 |access-date=2023-02-11|url-access=subscription }}.</ref> and Mulvey.<ref name=Mulvey>{{Cite journal |last=Mulvey |first=T |date=1962 |title=Origins and historical development of the electron microscope |url=https://iopscience.iop.org/article/10.1088/0508-3443/13/5/303 |journal=British Journal of Applied Physics |volume=13 |issue=5 |pages=197–207 |doi=10.1088/0508-3443/13/5/303 |issn=0508-3443|url-access=subscription }}</ref>

One effort was university based. In 1928, at the [[Technische Hochschule]] in Charlottenburg (now [[Technische Universität Berlin]]), {{ill|Adolf Matthias|de|Adolf Matthias (Elektrotechniker)}} (Professor of High Voltage Technology and Electrical Installations) appointed [[Max Knoll]] to lead a team of researchers to advance research on electron beams and cathode-ray oscilloscopes. The team consisted of several PhD students including [[Ernst Ruska]]. In 1931, Max Knoll and Ernst Ruska<ref name="Knoll1" /><ref name="Knoll2" /> successfully generated magnified images of mesh grids placed over an anode aperture. The device, a replicate of which is shown in [[#Figure 5|Figure 5]], used two  [[magnetic lens]]es to achieve higher magnifications, the first electron microscope. (Max Knoll died in 1969,<ref>{{Cite web |title=Max Knoll |url=https://www.ancientfaces.com/person/max-knoll-birth-1897-death-1969-europe/18955684 |access-date=2023-09-26 |website=AncientFaces |language=en}}</ref> so did not receive a share of the [[Nobel Prize in Physics]] in 1986.)

Apparently independent of this effort was work at [[Siemens-Schuckertwerke|Siemens-Schuckert]] by [[Reinhold Rudenberg]]. According to patent law (U.S. Patent No. 2058914<ref>{{Cite web |last=Rüdenberg |first=Reinhold |title=Apparatus for producing images of objects |url=https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/2058914 |access-date=24 February 2023 |website=Patent Public Search Basic}}</ref> and 2070318,<ref>{{Cite web |last=Rüdenberg |first=Reinhold |title=Apparatus for producing images of objects |url=https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/2070318 |access-date=24 February 2023 |website=Patent Public Search Basic}}</ref> both filed in 1932), he is the inventor of the electron microscope, but it is not clear when he had a working instrument. He stated in a very brief article in 1932<ref>{{Cite journal |last=Rodenberg |first=R. |date=1932 |title=Elektronenmikroskop |url=http://link.springer.com/10.1007/BF01505383 |journal=Die Naturwissenschaften |language=de |volume=20 |issue=28 |pages=522 |doi=10.1007/BF01505383 |bibcode=1932NW.....20..522R |s2cid=263996652 |issn=0028-1042|url-access=subscription }}</ref> that Siemens had been working on this for some years before the patents were filed in 1932, so his effort was parallel to the university effort. He died in 1961,<ref>{{Cite journal |date=April 1962 |title=Orbituary of Reinhold Rudenberg |url=https://pubs.aip.org/physicstoday/article/15/4/106/422766/Reinhold-Rudenberg |access-date=2023-09-26 |website=pubs.aip.org |doi=10.1063/1.3058109|doi-access=free |url-access=subscription }}</ref> so similar to Max Knoll, was not eligible for a share of the Nobel Prize.

These instruments could produce magnified images, but were not particularly useful for electron diffraction; indeed, the wave nature of electrons was not exploited during the development. Key for electron diffraction in microscopes was the advance in 1936 where {{ill|Hans Boersch|de}} showed that they could be used as micro-diffraction cameras with an aperture<ref>{{Cite journal |last=Boersch |first=H. |date=1936 |title=Über das primäre und sekundäre Bild im Elektronenmikroskop. II. Strukturuntersuchung mittels Elektronenbeugung |url=https://onlinelibrary.wiley.com/doi/10.1002/andp.19364190107 |journal=Annalen der Physik |language=de |volume=419 |issue=1 |pages=75–80 |doi=10.1002/andp.19364190107|bibcode=1936AnP...419...75B |url-access=subscription }}</ref>—the birth of [[#Selected area electron diffraction|selected area electron diffraction]].<ref name="HirschEtAl" />{{Rp|location=Chpt 5-6}}

Less controversial was the development of [[#Low-energy electron diffraction|LEED]]—the early experiments of Davisson and Germer used this approach.<ref name=DG1/><ref name=DG2/> As early as 1929 Germer investigated gas adsorption,<ref>{{Cite journal |last=Germer |first=L. H. |date=1929 |title=Eine Anwendung der Elektronenbeugung auf die Untersuchung der Gasadsorption |url=http://link.springer.com/10.1007/BF01375462 |journal=Zeitschrift für Physik |language=de |volume=54 |issue=5–6 |pages=408–421 |doi=10.1007/BF01375462 |bibcode=1929ZPhy...54..408G |s2cid=121097655 |issn=1434-6001|url-access=subscription }}</ref> and in 1932 Harrison E. Farnsworth probed single crystals of copper and silver.<ref>{{Cite journal |last=Farnsworth |first=H. E. |date=1932 |title=Diffraction of Low-Speed Electrons by Single Crystals of Copper and Silver |url=https://link.aps.org/doi/10.1103/PhysRev.40.684 |journal=Physical Review |language=en |volume=40 |issue=5 |pages=684–712 |doi=10.1103/PhysRev.40.684 |bibcode=1932PhRv...40..684F |issn=0031-899X|url-access=subscription }}</ref> However, the vacuum systems available at that time were not good enough to properly control the surfaces, and it took almost forty years before these became available.<ref name="VanHove">{{cite book |last1=Van Hove |first1=Michel A. |url=https://www.springer.com/gp/book/9783642827235 |title=Low-Energy Electron Diffraction |last2=Weinberg |first2=William H. |last3=Chan |first3=Chi-Ming |date=1986 |publisher=Springer-Verlag, Berlin Heidelberg New York |isbn=978-3-540-16262-9 |pages=13–426}}</ref><ref>{{Cite book |url=https://www.worldcat.org/oclc/7276396 |title=Fifty years of electron diffraction : in recognition of fifty years of achievement by the crystallographers and gas diffractionists in the field of electron diffraction |date=1981 |publisher=Published for the International Union of Crystallography by D. Reidel |editor=Goodman, P. (Peter) |isbn=90-277-1246-8 |location=Dordrecht, Holland |oclc=7276396}}</ref> Similarly, it was not until about 1965 that Peter B. Sewell and M. Cohen demonstrated the power of [[Electron diffraction#Reflection high-energy electron diffraction (RHEED)|RHEED]] in a system with a very well controlled vacuum.<ref>{{Cite journal |last1=Sewell |first1=P. B. |last2=Cohen |first2=M. |date=1965 |title=The Observation Of Gas Adsorption Phenomena By Reflection High-Energy Electron Diffraction |url=http://aip.scitation.org/doi/10.1063/1.1754284 |journal=Applied Physics Letters |language=en |volume=7 |issue=2 |pages=32–34 |doi=10.1063/1.1754284 |bibcode=1965ApPhL...7...32S |issn=0003-6951|url-access=subscription }}</ref>