View source for Electron microscope

{{short description|Type of microscope with electrons as a source of illumination}}
{{distinguish|Scanning tunneling microscope}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
[[File:TITAN.jpg|thumb|A modern transmission electron microscope (TITAN)]]An '''electron microscope''' is a [[microscope]] that uses a beam of [[electron]]s as a source of illumination. It uses [[electron optics]] that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing it to produce magnified images or [[electron diffraction]] patterns. As the wavelength of an electron can be up to 100,000 times smaller than that of visible light, electron microscopes have a much higher [[Angular resolution|resolution]] of about 0.1&nbsp;nm, which compares to about 200&nbsp;nm for [[optical microscope|light microscope]]s.<ref name="Encyclopaedia Britannica">{{cite web |title=Electron microscope |url=https://www.britannica.com/technology/electron-microscope |website=Encyclopaedia Britannica |access-date=June 26, 2024}}</ref> ''Electron microscope'' may refer to:
* [[Transmission electron microscopy|Transmission electron microscope]] (TEM) where swift electrons go through a thin sample
* [[Scanning transmission electron microscopy|Scanning transmission electron microscope]] (STEM) which is similar to TEM with a scanned electron probe
* [[Scanning electron microscope]] (SEM) which is similar to STEM, but with thick samples
* [[Electron microprobe]] similar to a SEM, but more for chemical analysis
* [[Low-energy electron microscopy|Low-energy electron microscope]] (LEEM), used to image surfaces
* [[Photoemission electron microscopy|Photoemission electron microscope]] (PEEM) which is similar to LEEM using electrons emitted from surfaces by photons
Additional details can be found in the above links. This article contains some general information mainly about transmission and scanning electron microscopes.

== History ==
{{See also|Transmission electron microscopy#History}}
Many developments laid the groundwork of the [[electron optics]] used in microscopes.<ref name="Calbick-1944">{{Cite journal | vauthors = Calbick CJ |date=1944 |title=Historical Background of Electron Optics |journal=Journal of Applied Physics |volume=15 |issue=10 |pages=685–690 |doi=10.1063/1.1707371 |bibcode=1944JAP....15..685C }}</ref> One significant step was the work of [[Heinrich Hertz|Hertz]] in 1883<ref name="Hertz-2019">{{cite book | vauthors = Hertz H | veditors = Mulligan JF |chapter = Introduction to Heinrich Hertz's Miscellaneous Papers (1895) by Philipp Lenard |date=2019 | title = Heinrich Rudolf Hertz (1857-1894) : a collection of articles and addresses |pages=87–88 |publisher=Routledge |doi=10.4324/9780429198960-4 |isbn=978-0-429-19896-0 }}</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 the electrons by an axial magnetic field by [[Emil Wiechert]] in 1899,<ref name="Wiechert-1899">{{Cite journal | vauthors = Wiechert E |date=1899 |title=Experimentelle Untersuchungen über die Geschwindigkeit und die magnetische Ablenkbarkeit der Kathodenstrahlen |trans-title=Experimental Investigations on the Velocity and Magnetic Deflection of Cathode Rays |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 | vauthors = Wehnelt A |date=1905 |title=X. On the discharge of negative ions by glowing metallic oxides, and allied phenomena |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |volume=10 |issue=55 |pages=80–90 |doi=10.1080/14786440509463347 }}</ref> and the development of the electromagnetic lens in 1926 by [[Hans Busch]].<ref name="Busch-1926">{{Cite journal | vauthors = Busch H |date=1926 |title=Berechnung der Bahn von Kathodenstrahlen im axialsymmetrischen elektromagnetischen Felde |trans-title=Calculation of the trajectory of cathode rays in an axially symmetric electromagnetic field |journal=Annalen der Physik |language=de |volume=386 |issue=25 |pages=974–993 |doi=10.1002/andp.19263862507 |bibcode=1926AnP...386..974B }}</ref> According to [[Dennis Gabor]], the physicist [[Leo Szilard|Leó Szilárd]] tried in 1928 to convince him to build an electron microscope, for which Szilárd had filed a patent.<ref name="Dannen-1998">Dannen, Gene (1998)  [http://www.dannen.com/budatalk.html Leo Szilard the Inventor: A Slideshow (1998, Budapest, conference talk)]. dannen.com</ref>[[File:Ernst Ruska Electron Microscope - Deutsches Museum - Munich-edit.jpg|thumb|Reproduction of an early electron microscope constructed by [[Ernst Ruska]] in the 1930s]] To this day the issue of who invented the transmission electron microscope is controversial.<ref name="Mulvey-1962">{{Cite journal | vauthors = Mulvey T |date=1962 |title=Origins and historical development of the electron microscope |journal=British Journal of Applied Physics |volume=13 |issue=5 |pages=197–207 |doi=10.1088/0508-3443/13/5/303 }}</ref><ref name="Tao-2018">{{Cite book | vauthors = Tao Y |title=Proceedings of the 3rd International Conference on Contemporary Education, Social Sciences and Humanities (ICCESSH 2018) |chapter=A Historical Investigation of the Debates on the Invention and Invention Rights of Electron Microscope |date=2018 |chapter-url=https://www.atlantis-press.com/proceedings/iccessh-18/25898208 | series = Advances in Social Science, Education and Humanities Research |publisher=Atlantis Press |pages=1438–1441 |doi=10.2991/iccessh-18.2018.313 |isbn=978-94-6252-528-3}}</ref><ref name="Freundlich-1963">{{cite journal | vauthors = Freundlich MM | title = Origin of the Electron Microscope | journal = Science | volume = 142 | issue = 3589 | pages = 185–188 | date = October 1963 | pmid = 14057363 | doi = 10.1126/science.142.3589.185 | bibcode = 1963Sci...142..185F }}</ref><ref name="Rüdenberg-2010">{{cite book |doi=10.1016/s1076-5670(10)60005-5 |title=Origin and Background of the Invention of the Electron Microscope |series=Advances in Imaging and Electron Physics |date=2010 |volume=160 |pages=171–205 |isbn=978-0-12-381017-5 | vauthors = Rüdenberg R }}.</ref> In 1928, at the [[Technische Hochschule]] in Charlottenburg (now [[Technische Universität Berlin]]), Adolf Matthias (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="Knoll-1932a">{{Cite journal | vauthors = Knoll M, Ruska E |date=1932 |title=Beitrag zur geometrischen Elektronenoptik. I |journal=Annalen der Physik |volume=404 |issue=5 |pages=607–640 |doi=10.1002/andp.19324040506 |bibcode=1932AnP...404..607K }}</ref><ref name="Knoll-1932b">{{Cite journal | vauthors = Knoll M, Ruska E |date=1932 |title=Das Elektronenmikroskop |journal=Zeitschrift für Physik |language=de |volume=78 |issue=5–6 |pages=318–339 |doi=10.1007/BF01342199 |bibcode=1932ZPhy...78..318K }}</ref> successfully generated magnified images of mesh grids placed over an anode aperture. The device, a replicate of which is shown in the figure, used two magnetic lenses to achieve higher magnifications, the first electron microscope. (Max Knoll died in 1969, so did not receive a share of the 1986 [[Nobel Prize|Nobel prize]] for the invention of electron microscopes.)

Apparently independent of this effort was work at [[Siemens-Schuckertwerke|Siemens-Schuckert]] by [[Reinhold Rudenberg|Reinhold Rüdenberg]]. According to patent law (U.S. Patent No. 2058914<ref name="Rüdenberg-1936">{{Cite web | vauthors = Rüdenberg R |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 | vauthors = Rüdenberg R |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 name="Rodenberg-1932">{{cite journal |last1=Rüdenberg |first1=R. |title=Elektronenmikroskop |journal=Die Naturwissenschaften |date=July 1932 |volume=20 |issue=28 |pages=522 |doi=10.1007/BF01505383 |bibcode=1932NW.....20..522R }}</ref> that Siemens had been working on this for some years before the patents were filed in 1932, claiming that his effort was parallel to the university development. He died in 1961, so similar to Max Knoll, was not eligible for a share of the 1986 Nobel prize.<ref name="LEO Electron Microscopy">{{Cite web |title=History of Electron Microscope |url=https://www.leo-em.co.uk/history-of-electron-microscope.html |website=LEO Electron Microscopy |access-date=June 26, 2024}}</ref>

In the following year, 1933, Ruska and Knoll built the first electron microscope that exceeded the resolution of an optical (light) microscope.<ref name="Ruska, Ernst-1986">{{cite web |author=Ruska, Ernst |year=1986 |title=Ernst Ruska Autobiography |url=http://nobelprize.org/nobel_prizes/physics/laureates/1986/ruska-autobio.html |access-date=2010-01-31 |publisher=Nobel Foundation}}</ref>  Four years later, in 1937, Siemens financed the work of Ernst Ruska and [[Bodo von Borries]], and employed [[Helmut Ruska]], Ernst's brother, to develop applications for the microscope, especially with biological specimens.<ref name="Ruska, Ernst-1986" /><ref name="Kruger-2000">{{cite journal | vauthors = Kruger DH, Schneck P, Gelderblom HR | title = Helmut Ruska and the visualisation of viruses | journal = Lancet | volume = 355 | issue = 9216 | pages = 1713–1717 | date = May 2000 | pmid = 10905259 | doi = 10.1016/S0140-6736(00)02250-9 }}</ref> Also in 1937, [[Manfred von Ardenne]] pioneered the [[scanning electron microscope]].<ref>{{cite journal | vauthors = Von Ardenne M, Beischer D |title=Untersuchung von Metalloxyd-Rauchen mit dem Universal-Elektronenmikroskop |trans-title=Investigation of metal oxide smoking with the universal electron microscope |language=de |journal=Zeitschrift für Elektrochemie und Angewandte Physikalische Chemie |date=1940 |volume=46 |issue=4 |pages=270–277 |doi=10.1002/bbpc.19400460406 }}</ref> Siemens produced the first commercial electron microscope in 1938.<ref>[http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/materials/public/ElectronMicroscope/EM_HistOverview.htm History of electron microscopy, 1931–2000]. Authors.library.caltech.edu (2002-12-10). Retrieved on 2017-04-29.</ref> The first North American electron microscopes were constructed in the 1930s, at the [[Washington State University]] by Anderson and Fitzsimmons <ref>{{Cite web|url=https://news.wsu.edu/2018/05/14/wsu-home-north-americas-first-electron-microscope/|title = North America's first electron microscope}}</ref>  and at the [[University of Toronto]] by [[Eli Franklin Burton]] and students Cecil Hall, [[James Hillier]], and Albert Prebus. Siemens produced a transmission electron microscope (TEM) in 1939.<ref>{{cite web |url=http://web.mit.edu/Invent/iow/hillier.html |archive-url=https://web.archive.org/web/20030823110629/http://web.mit.edu/invent/iow/hillier.html |url-status=dead |archive-date=2003-08-23 |title=James Hillier|website=Inventor of the Week: Archive |date=2003-05-01 |access-date=2010-01-31}}</ref> Although current transmission electron microscopes are capable of two million times magnification, as scientific instruments they remain similar but with improved optics.

In the 1940s, high-resolution electron microscopes were developed, enabling greater magnification and resolution.<ref>{{cite book | vauthors = Hawkes PW |title=The Beginnings of Electron Microscopy. Part 1 |date=2021 |publisher=Academic Press |location=London San Diego, CA Cambridge, MA Oxford |isbn=978-0-323-91507-6}}</ref> By 1965, [[Albert Crewe]] at the [[University of Chicago]] introduced the scanning transmission electron microscope using a [[Field emission gun|field emission source]],<ref>{{Cite journal |last1=Crewe |first1=A. V. |last2=Eggenberger |first2=D. N. |last3=Wall |first3=J. |last4=Welter |first4=L. M. |date=1968-04-01 |title=Electron Gun Using a Field Emission Source |journal=Review of Scientific Instruments |volume=39 |issue=4 |pages=576–583 |doi=10.1063/1.1683435 |bibcode=1968RScI...39..576C }}</ref> enabling scanning microscopes at high resolution.<ref>{{cite journal | vauthors = Crewe AV | title = Scanning electron microscopes: is high resolution possible? | journal = Science | volume = 154 | issue = 3750 | pages = 729–738 | date = November 1966 | pmid = 17745977 | doi = 10.1126/science.154.3750.729 | bibcode = 1966Sci...154..729C }}</ref> By the early 1980s improvements in mechanical stability as well as the use of higher accelerating voltages enabled imaging of materials at the atomic scale.<ref>{{Cite journal |last1=Smith |first1=David J. |last2=Camps |first2=R. A. |last3=Freeman |first3=L. A. |last4=Hill |first4=R. |last5=Nixon |first5=W. C. |last6=Smith |first6=K. C. A. |date=May 1983 |title=Recent improvements to the Cambridge University 600 kV High Resolution Electron Microscope |journal=Journal of Microscopy |volume=130 |issue=2 |pages=127–136 |doi=10.1111/j.1365-2818.1983.tb04211.x }}</ref><ref name="Spence-2013">{{cite book |doi=10.1093/acprof:oso/9780199668632.001.0001 |title=High-Resolution Electron Microscopy |date=2013 |last1=Spence |first1=John C. H. |isbn=978-0-19-966863-2 }}{{page needed|date=January 2025}}</ref> In the 1980s, the [[field emission gun]] became common for electron microscopes, improving the image quality due to the additional coherence and lower chromatic aberrations. The 2000s were marked by advancements in aberration-corrected electron microscopy, allowing for significant improvements in resolution and clarity of images.<ref>{{cite journal |last1=Hawkes |first1=P. W. |title=Aberration correction past and present |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |date=28 September 2009 |volume=367 |issue=1903 |pages=3637–3664 |doi=10.1098/rsta.2009.0004 |pmid=19687058 |bibcode=2009RSPTA.367.3637H }}</ref><ref>{{cite journal |last1=Rose |first1=H. H. |title=Historical aspects of aberration correction |journal=Journal of Electron Microscopy |date=June 2009 |volume=58 |issue=3 |pages=77–85 |doi=10.1093/jmicro/dfp012 |pmid=19254915 }}</ref>

== Types of electron microscopes ==

[[File:Transmission Electron Microscope operating principle.ogg|thumb|upright=1.5|Operating principle of a transmission electron microscope]]

=== Transmission electron microscope (TEM) ===
{{Main|Transmission electron microscope}}
[[File:Electron_Microscope.png|thumb|Transmission Electron Microscope]]
The original form of the electron microscope, the [[transmission electron microscope]] (TEM), uses a [[high voltage]] [[electron beam]] to illuminate the specimen and create an image. An electron beam is produced by an [[electron gun]], with the electrons typically having energies in the range 20 to 400 keV, focused by [[Electromagnetism|electromagnetic]] lenses, and transmitted through a thin specimen. When it emerges from the specimen, the electron beam carries information about the structure of the specimen that is then magnified by the lenses of the microscope. The spatial variation in this information (the "image") may be viewed by projecting the magnified electron image onto a [[Detectors for transmission electron microscopy|detector]]. For example, the image may be viewed directly by an operator using a fluorescent viewing screen coated with a [[phosphor]] or [[scintillator]] material such as [[zinc sulfide]]. More commonly a high-resolution phosphor is coupled by means of a lens optical system or a [[fibre optic]] light-guide to the sensor of a [[digital camera]]. A different approach is to use a [[Detectors for transmission electron microscopy#Direct electron detectors|direct electron detector]] which has no scintillator, which addresses some of the limitations of scintillator-coupled cameras.<ref>{{cite journal | vauthors = Cheng Y, Grigorieff N, Penczek PA, Walz T | title = A primer to single-particle cryo-electron microscopy | journal = Cell | volume = 161 | issue = 3 | pages = 438–449 | date = April 2015 | pmid = 25910204 | pmc = 4409659 | doi = 10.1016/j.cell.2015.03.050 }}</ref>

For many years the resolution of TEMs was limited by aberrations of the electron optics, primarily the [[spherical aberration]]. In most recent instruments hardware correctors can reduce spherical aberration and other aberrations, improving the resolution in [[high-resolution transmission electron microscopy]] (HRTEM) to below 0.5 [[angstrom]] (50 [[picometre]]s),<ref name="Erni-2009">{{cite journal | vauthors = Erni R, Rossell MD, Kisielowski C, Dahmen U | title = Atomic-resolution imaging with a sub-50-pm electron probe | journal = Physical Review Letters | volume = 102 | issue = 9 | article-number = 096101 | date = March 2009 | pmid = 19392535 | doi = 10.1103/PhysRevLett.102.096101 | bibcode = 2009PhRvL.102i6101E | osti = 960283 | url = https://www.escholarship.org/uc/item/3cs0m4vr }}</ref> enabling magnifications of more than 50 million times.<ref>{{cite web|url=http://www.sc.doe.gov/bes/scale_of_things.html |title=The Scale of Things |date=2006-05-26 |publisher=Office of Basic Energy Sciences, U.S. Department of Energy |access-date=2010-01-31 |url-status=dead |archive-url=https://web.archive.org/web/20100201175106/http://www.sc.doe.gov/bes/scale_of_things.html |archive-date=2010-02-01 }}</ref> The ability of HRTEM to determine the positions of atoms within materials is useful for many areas of research and development.<ref>{{cite web| vauthors = O'Keefe MA, Allard LF |title = Sub-Ångstrom Electron Microscopy for Sub-Ångstrom Nano-Metrology |url=http://www.osti.gov/bridge/servlets/purl/821768-E3YVgN/native/821768.pdf |publisher=Information Bridge: DOE Scientific and Technical Information – Sponsored by OSTI |date=2004-01-18}}</ref>

=== Scanning electron microscope (SEM) ===
[[File:Scanning Electron Microscope.ogv|thumb|upright=1.5|right|Operating principle of a scanning electron microscope]]
{{Main|Scanning electron microscope}}
An SEM produces images by probing the specimen with a focused electron beam that is scanned across the specimen ([[raster scan]]ning). When the electron beam interacts with the specimen, it loses energy and is scattered in different directions by a variety of mechanisms. These interactions lead to, among other events, emission of [[secondary emission|low-energy secondary electrons]] and high-energy backscattered electrons, light emission ([[cathodoluminescence]]) or [[X-ray]] emission. All of these signals carrying information about the specimen, such as the surface topography and composition. The image displayed when using an SEM shows the variation in the intensity of any of these signals as an image. In these each position in the image corresponding to a position of the beam on the specimen when the signal was generated.<ref name="Kohl-2008" />{{RP|pages=1-15}}
[[File:TESCAN_S8000X.jpg|thumb|TESCAN S8000X SEM]]
SEMs are different from TEMs in that they use electrons with much lower energy, generally below 20 keV,<ref>{{Cite journal | vauthors = Dusevich V, Purk J, Eick J |date= January 2010 |title=Choosing the Right Accelerating Voltage for SEM (An Introduction for Beginners) |journal=Microscopy Today |volume=18 |issue=1 |pages=48–52 |doi=10.1017/s1551929510991190 }}</ref> while TEMs generally use electrons with energies in the range of 80-300 keV.<ref name="Saha-2022" /> Thus, the electron sources and optics of the two microscopes have different designs, and they are normally separate instruments.<ref>{{Cite web |date=2022-04-07 |title=Electron Microscopy {{!}} Thermo Fisher Scientific - US |url=https://www.thermofisher.com/us/en/home/electron-microscopy.html |access-date=2024-07-13 |archive-url=https://web.archive.org/web/20220407190819/https://www.thermofisher.com/us/en/home/electron-microscopy.html |archive-date=2022-04-07 }}</ref>

=== Scanning transmission electron microscope (STEM) ===
{{Main|Scanning transmission electron microscopy}}
A STEM combines features of both a TEM and a SEM by rastering a focused incident probe across a specimen, but now mainly using the electrons which are transmitted through the sample. Many types of imaging are common to both TEM and STEM, but some such as [[annular dark-field imaging]] and other analytical techniques are much easier to perform with higher spatial resolutions in a STEM instrument. One drawback is that image data is acquired in serial rather than in parallel fashion.<ref name="Kohl-2008">{{cite book |last1=Kohl |first1=Helmut |title=Transmission Electron Microscopy |last2=Reimer |first2=Ludwig |date=2008 |publisher=Springer |isbn=978-0-387-40093-8 |series=Springer Series in Optical Sciences |volume=36 |pages= |chapter=Elements of a Transmission Electron Microscope |doi=10.1007/978-0-387-40093-8_4}}</ref>{{Rp|pages=75–138}}

== Main operating modes ==
[[File:Ant SEM.jpg|thumb|right|An image of an [[ant]] in an SEM]]The most common methods of obtaining images in an electron microscope involve selecting different directions for the electrons that have been transmitted through a sample, and/or electrons of different energies. There are a very large number of methods of doing this, although not all are very common.

=== Secondary electrons ===
[[File:Electron-matter_interaction_volume_and_various_types_of_signal_generated_-_v2.svg|thumb|Electron–matter interaction volume and types of signal generated in a SEM]]
In a SEM the signals result from interactions of the electron beam with atoms within the sample. The most common mode is to use the [[secondary electrons]] (SE) to produce images. Secondary electrons have very low energies, on the order of 50 [[Electronvolt|eV]], which limits their [[Inelastic mean free path|mean free path]] in solid matter to a few [[nanometer]]s below the sample surface.<ref name="Goldstein-2003" />  The electrons are detected by an [[Everhart–Thornley detector]],<ref name="Everhart-1960">{{cite journal |last=Everhart |first=T. E. |author2=Thornley, R. F. M. |year=1960 |title=Wide-band detector for micro-microampere low-energy electron currents |url=http://authors.library.caltech.edu/12086/1/EVEjsi60.pdf |journal=Journal of Scientific Instruments |volume=37 |issue=7 |pages=246–248 |bibcode=1960JScI...37..246E |doi=10.1088/0950-7671/37/7/307}}</ref> which is a type of collector-[[scintillator]]-[[photomultiplier]] system. The signal from secondary electrons tends to be highly localized at the point of impact of the primary electron beam, making it possible to collect images of the sample surface with a resolution of better than 1 [[Nanometre|nm]], and with specialized instruments at the atomic scale.<ref>{{Cite journal |last1=Ciston |first1=J. |last2=Brown |first2=H. G. |last3=D'Alfonso |first3=A. J. |last4=Koirala |first4=P. |last5=Ophus |first5=C. |last6=Lin |first6=Y. |last7=Suzuki |first7=Y. |last8=Inada |first8=H. |last9=Zhu |first9=Y. |last10=Allen |first10=L. J. |last11=Marks |first11=L. D. |date=2015-06-17 |title=Surface determination through atomically resolved secondary-electron imaging |journal=Nature Communications |language=en |volume=6 |issue=1 |article-number=7358 |doi=10.1038/ncomms8358 |issn=2041-1723 |pmc=4557350 |pmid=26082275}}</ref>

The brightness of the signal depends on the number of secondary electrons reaching the [[Sensor|detector]]. If the beam enters the sample perpendicular to the surface, then the electrons come out symmetrically about the axis of the beam. As the angle of incidence increases, the interaction volume from which they cone increases and the "escape" distance from one side of the beam decreases, resulting in more secondary electrons being emitted from the sample. Thus steep surfaces and edges tend to be brighter than flat surfaces, which results in images with a well-defined, three-dimensional appearance that is similar to a reflected light image.<ref name="Goldstein-2003" />

=== Backscattered electrons ===
Backscattered electrons (BSE) are those emitted back out from the specimen due to beam-specimen interactions where the electrons undergo [[Elastic scattering|elastic]] and [[Inelastic scattering|inelastic]] scattering. They are conventionally defined as having energies from 50 eV up to the energy of the primary beam. Backscattered electrons can be used for both imaging and to form an [[electron backscatter diffraction]] (EBSD) image, the latter can be used to determine the crystallography of the specimen.<ref name="Goldstein-2003" />[[File:EBSD_(001)_Si.png|thumb|Electron backscatter diffraction pattern for (001) single crystal silicon crystals taken at 20kV using Oxford S2 detector]]

Heavy elements (high atomic number) backscatter electrons more strongly than light elements (low atomic number), and thus appear brighter in the image, BSE images can therefore be used to detect areas with different chemical compositions.<ref name="Goldstein-2003" />  To optimize the signal, dedicated backscattered electron detectors are positioned above the sample in a "doughnut" type arrangement, concentric with the electron beam, maximizing the solid angle of collection. BSE detectors are usually either scintillator or semiconductor types. When all parts of the detector are used to collect electrons symmetrically about the beam, atomic number contrast is produced. However, strong topographic contrast is produced by collecting back-scattered electrons from one side above the specimen using an asymmetrical, directional BSE detector; the resulting contrast appears as if there was illumination of the topography from that side. Semiconductor detectors can be made in radial segments that can be switched in or out to control the type of contrast produced and its directionality.<ref name="Goldstein-2003" />

=== Diffraction contrast imaging ===
Diffraction contrast uses the variation in either or both the direction of diffracted electrons or their amplitude as a function of position as the contrast mechanism. It is one of the simplest ways to image in a transmission electron microscope, and widely used.

The idea is to use an objective aperture below the sample and select only one or a range of different diffracted directions, then use these to form an image. When the aperture includes the incident beam direction the images are called ''bright field'', since in the absence of any sample the field of view would be uniformly bright. When the aperture excludes the incident beam the images are called ''dark field'', since similarly without a sample the image would be uniformly dark.<ref name="HirschEtAl">{{Cite book |last1=Hirsch |first1=P. B. |title=Electron microscopy of thin crystals |last2=Howie |first2=A. |last3=Nicholson |first3=R. B. |last4=Pashley |first4=D. W. |last5=Whelan |first5=M. J. |date=1965 |publisher=Butterworths |isbn=0-408-18550-3 |location=London |oclc=2365578}}</ref><ref>{{Cite journal |last=Reimer |first=Ludwig |date=1997 |title=Transmission Electron Microscopy |url=https://doi.org/10.1007/978-3-662-14824-2 |journal=Springer Series in Optical Sciences |volume=36 |doi=10.1007/978-3-662-14824-2 |isbn=978-3-662-14826-6 |issn=0342-4111|url-access=subscription }}</ref> One variant of this is called [[weak-beam dark-field microscopy]], and can be used to obtain high resolution images of defects such as dislocations.<ref>{{Cite journal |last1=Cockayne |first1=D. J. H. |last2=Ray |first2=I. L. F. |last3=Whelan |first3=M. J. |date=1969-12-01 |title=Investigations of dislocation strain fields using weak beams |url=https://www.tandfonline.com/doi/abs/10.1080/14786436908228210 |journal=The Philosophical Magazine |volume=20 |issue=168 |pages=1265–1270 |doi=10.1080/14786436908228210 |bibcode=1969PMag...20.1265C |issn=0031-8086|url-access=subscription }}</ref>

=== High resolution imaging ===
{{Main|High-resolution transmission electron microscopy|Annular dark-field imaging}}
[[File:CuTe-HRTEM.jpg|thumb|CuTe High resolution image]]
In high-resolution transmission electron microscopy (also sometimes called high-resolution electron microscopy) a number of different diffracted beams are allowed through the objective aperture. These interfere, leading to images which represent the atomic structure of the material. These can include the incident beam direction, or with scanning transmission electron microscopes they typically are for a range of diffracted beams excluding the incident beam.<ref name="Spence-2013" /> Depending upon how thick the samples are and the [[Optical aberration|aberrations]] of the microscope, these images can either be directly interpreted in terms of the positions of columns of atoms, or require a more careful analysis using calculations of the [[Multislice|multiple scattering]] of the electrons<ref>{{Cite journal |last=Ishizuka |first=Kazuo |date=2004-02-01 |title=FFT Multislice Method—The Silver Anniversary |url=https://academic.oup.com/mam/article-abstract/10/1/34/6912350?redirectedFrom=fulltext |journal=Microscopy and Microanalysis |volume=10 |issue=1 |pages=34–40 |doi=10.1017/S1431927604040292 |issn=1431-9276|url-access=subscription }}</ref> and the effect of the [[contrast transfer function]] of the microscope.<ref>{{Cite journal |last=Wade |first=R. H. |date=1992-10-01 |title=A brief look at imaging and contrast transfer |url=https://linkinghub.elsevier.com/retrieve/pii/0304399192900118 |journal=Ultramicroscopy |volume=46 |issue=1 |pages=145–156 |doi=10.1016/0304-3991(92)90011-8 |issn=0304-3991|url-access=subscription }}</ref>{{Main|Electron holography|4D scanning transmission electron microscopy|l2 = 4D STEM}}

There are many other imaging variants that can also to lead to atomic level information. [[Electron holography]] uses the interference of electrons which have been through the sample and a reference beam.<ref>{{Cite journal |last=Cowley |first=J. M. |date=1992-06-01 |title=Twenty forms of electron holography |url=https://linkinghub.elsevier.com/retrieve/pii/0304399192902134 |journal=Ultramicroscopy |volume=41 |issue=4 |pages=335–348 |doi=10.1016/0304-3991(92)90213-4 |issn=0304-3991|url-access=subscription }}</ref> [[4D scanning transmission electron microscopy|4D STEM]] collects diffraction data at each point using a scanning instrument, then processes them to produce different types of images.<ref>{{Cite journal |last=Ophus |first=Colin |date=2019-06-01 |title=Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM): From Scanning Nanodiffraction to Ptychography and Beyond |journal=Microscopy and Microanalysis |volume=25 |issue=3 |pages=563–582 |doi=10.1017/S1431927619000497 |issn=1431-9276|doi-access=free }}</ref>

=== X-ray microanalysis ===
{{Main|Energy-dispersive X-ray spectroscopy}}
[[File:EDS_-_Rimicaris_exoculata.png|thumb|class=skin-invert-image|EDS spectrum of the mineral crust of the vent shrimp ''[[Rimicaris exoculata]]''<ref>{{cite journal |author=Corbari, L |display-authors=etal |year=2008 |title=Iron oxide deposits associated with the ectosymbiotic bacteria in the hydrothermal vent shrimp Rimicaris exoculata |journal=Biogeosciences |volume=5 |issue=5 |pages=1295–1310 |bibcode=2008BGeo....5.1295C |doi=10.5194/bg-5-1295-2008 |doi-access=free}}</ref> Most of these peaks are [[K-alpha]] and [[K-beta]] lines. One peak is from the L shell of iron.]]
X-ray microanalysis is a method of obtaining local chemical information within electron microscopes of all types, although it is most commonly used in scanning instruments. When high energy electrons interact with atoms they can knock out electrons, particularly those in the [[inner shell]]s and [[core electrons]]. These are then filled by [[valence electron]], and the energy difference between the valence and core states can be converted into an [[x-ray]] which is detected by a spectrometer. The energies of these x-rays is somewhat specific to the atomic species, so local chemistry can be probed.<ref name="Goldstein-2003">{{Cite book |last=Goldstein |first=Joseph |url=https://books.google.com/books?id=ruF9DQxCDLQC |title=Scanning Electron Microscopy and X-Ray Microanalysis: Third Edition |date=2003-01-31 |publisher=Springer US |isbn=978-0-306-47292-3 |language=en}}</ref>

=== EELS ===
{{Main|Electron energy loss spectroscopy}}
[[File:Electron_energy_loss_spectrum_feature_overview.svg|thumb|class=skin-invert-image|Experimental electron energy loss spectrum, showing the major features: zero-loss peak, plasmon peaks and core loss edge.]]
Similar to X-ray microanalysis, the energies of electrons which have transmitted through a sample can be analyzed and yield information ranging from details of the local electronic structure to chemical information.<ref>{{Citation |last=Egerton |first=Ray F. |title=An Introduction to Electron Energy-Loss Spectroscopy |date=1986 |work=Electron Energy-Loss Spectroscopy in the Electron Microscope |pages=1–25 |url=https://doi.org/10.1007/978-1-4615-6887-2_1 |access-date=2025-02-25 |place=Boston, MA |publisher=Springer US |doi=10.1007/978-1-4615-6887-2_1 |isbn=978-1-4615-6889-6|url-access=subscription }}</ref>

=== Electron diffraction ===
{{Main| Electron diffraction}}
Transmission electron microscopes can be used in [[electron diffraction]] mode where a map of the angles of the electrons leaving the sample is produced. The advantages of electron diffraction over [[X-ray crystallography]] are primarily in the size of the crystals. In X-ray crystallography, crystals are commonly visible by the naked eye and are generally in the hundreds of micrometers in length. In comparison, crystals for electron diffraction must be less than a few hundred nanometers in thickness, and have no lower boundary of size. Additionally, electron diffraction is done on a TEM, which can also be used to obtain other types of information, rather than requiring a separate instrument.<ref>{{Cite book |last=Cowley |first=J. M. |author-link=John M. Cowley |title=Diffraction physics |date=1995 |publisher=Elsevier |isbn=978-0-444-82218-5 |edition=3rd |series=North Holland personal library |location=Amsterdam}}</ref><ref name="Saha-2022">{{cite journal | vauthors = Saha A, Nia SS, Rodríguez JA | title = Electron Diffraction of 3D Molecular Crystals | journal = Chemical Reviews | volume = 122 | issue = 17 | pages = 13883–13914 | date = September 2022 | pmid = 35970513 | pmc = 9479085 | doi = 10.1021/acs.chemrev.1c00879 }}</ref>
[[File:CBEDThickness.png|thumb|Variations in CBED with thickness for Si (001)]]
{{Main|Convergent beam electron diffraction|Precession electron diffraction}}

There are many variants on electron diffraction, depending upon exactly what type of illumination conditions are used. If a parallel beam is used with an aperture to limit the region exposed to the electrons then sharp diffraction features are normally observed, a technique called [[Electron diffraction#Selected area electron diffraction|selected area electron diffraction]]. This is often the main technique used. Another common approach uses conical illumination and is called [[convergent beam electron diffraction]] (CBED). This is good for determining the symmetry of materials. A third is [[precession electron diffraction]], where a parallel beam is spun around a large angle, producing a type of average diffraction pattern.<ref name="Original">{{cite journal |last1=Vincent |first1=R. |last2=Midgley |first2=P.A. |year=1994 |title=Double conical beam-rocking system for measurement of integrated electron diffraction intensities |journal=Ultramicroscopy |volume=53 |issue=3 |pages=271–82 |doi=10.1016/0304-3991(94)90039-6}}</ref> These often have less multiple scattering.<ref name="thesis">Own, C. S.: PhD thesis, System Design and Verification of the Precession Electron Diffraction Technique, Northwestern University, 2005,http://www.numis.northwestern.edu/Research/Current/precession.shtml</ref>

=== Other electron microscope techniques ===

* [[Cathodoluminescence]] - analysing photons due to the electron beam
* [[Charge contrast imaging]] - using how charging varies with position to produce images
* [[Cryogenic electron microscopy|CryoEM]] - using frozen samples, almost always biological samples
* [[Electron backscatter diffraction|EBSD]] - using the back-scattered electrons, typically in a SEM
** [[Transmission Kikuchi diffraction|TKD]] - using the [[Kikuchi lines (physics)|Kikuchi lines]] in diffraction patterns
* [[Electron channelling contrast imaging|ECCI]] - using contrast due to electron channelling
* [[Electron beam-induced current|EBIC]] - measuring the current produced as a function of the position of a small beam
* [[Electron tomography]] - methods to produce 3D information by combining images
* [[Fluctuation electron microscopy|FEM]] - technique to interrogate nanocrystalline materials
* [[Immune electron microscopy]] - the use of electron microscopy in immunology
* [[Geometric phase analysis]] - a method to analyze high-resolution images
* [[Serial block-face scanning electron microscopy]] - a way to produce 3D information from many images
* [[Wavelength-dispersive X-ray spectroscopy|WDXS]] - higher precision detection of x-rays to analyze local chemistry

== Aberration corrected instruments ==
[[File:Stem1.JPG|thumb|Scanning transmission electron microscope equipped with a 3rd-order spherical aberration corrector]]
{{Main|Aberration-corrected transmission electron microscopy}}
Aberration-corrected transmission electron microscopy (AC-TEM) is the general term for electron microscopes where [[Electro-optics|electro optical]] components are introduced to reduce the [[Optical aberration|aberrations]] that would otherwise limit the [[Image resolution|resolution]] of the images. Historically electron microscopes had quite severe aberrations, and until about the start of the 21st century the resolution was limited, able to image the atomic structure of materials if the [[Atom|atoms]] were far enough apart.<ref>{{Cite journal |last=Smith |first=David J |date=1997-12-01 |title=The realization of atomic resolution with the electron microscope |url=https://doi.org/10.1088%2F0034-4885%2F60%2F12%2F002 |journal=Reports on Progress in Physics |volume=60 |issue=12 |pages=1513–1580 |doi=10.1088/0034-4885/60/12/002 |issn=0034-4885|url-access=subscription }}</ref> Around the turn of the century the electron optical components were coupled with computer control of the lenses and their alignment, enabling correction of aberrations. The first demonstration of aberration correction in TEM mode was by [[Harald Rose]] and [[Maximilian Haider]] in 1998 using a hexapole corrector, and in STEM mode by [[Ondrej Krivanek]] and Niklas Dellby in 1999 using a quadrupole/octupole corrector.<ref name="Pennycook-2012">{{Cite journal |last=Pennycook |first=S. J. |date=2012-12-01 |title=Seeing the atoms more clearly: STEM imaging from the Crewe era to today |url=https://www.sciencedirect.com/science/article/pii/S0304399112001076 |journal=Ultramicroscopy |series=Albert Victor Crewe Memorial Issue |volume=123 |pages=28–37 |doi=10.1016/j.ultramic.2012.05.005 |issn=0304-3991 |pmid=22727567|url-access=subscription }}</ref>

As of 2025 correction of geometric [[Spherical aberration|aberrations]] is standard in many commercial electron microscopes, and they are extensively used in many different areas of science.<ref>{{Cite book |last=Erni |first=Rolf |url=https://books.google.com/books?id=Gsw7DQAAQBAJ |title=Aberration-corrected Imaging In Transmission Electron Microscopy: An Introduction |date=2015-03-23 |edition=2nd |publisher=World Scientific Publishing Company |isbn=978-1-78326-530-5 |language=en}}</ref><ref>{{Cite journal |last=Rose |first=Harald |date=2006-07-01 |title=Aberration correction in electron microscopy |url=https://www.degruyterbrill.com:443/document/doi/10.1515/ijmr-2006-0143/html |journal=International Journal of Materials Research |language=en |volume=97 |issue=7 |pages=885–889 |doi=10.1515/ijmr-2006-0143 |issn=2195-8556|url-access=subscription }}</ref> Similar correctors have also been used at much lower energies for [[LEEM]] instruments.<ref>{{Cite journal |last1=Tromp |first1=R.M. |last2=Hannon |first2=J.B. |last3=Ellis |first3=A.W. |last4=Wan |first4=W. |last5=Berghaus |first5=A. |last6=Schaff |first6=O. |date=June 2010 |title=A new aberration-corrected, energy-filtered LEEM/PEEM instrument. I. Principles and design |url=https://linkinghub.elsevier.com/retrieve/pii/S0304399110000835 |journal=Ultramicroscopy |language=en |volume=110 |issue=7 |pages=852–861 |doi=10.1016/j.ultramic.2010.03.005 |pmid=20395048|url-access=subscription }}</ref>

== Sample preparation ==
[[File:Golden insect 01 Pengo.jpg|thumb|An insect [[sputter coating|coated in gold]] for viewing with a [[Scanning electron microscope|scanning electron microscope (SEM)]]]]
{{Main|Transmission electron microscopy#Sample preparation|Ultramicrotomy|Staining|Cryofixation|Chemical milling|Sputtering|
label 1=TEM Sample preparation}}
Samples for electron microscopes mostly cannot be observed directly. The samples need to be prepared to stabilize the sample and enhance contrast. Preparation techniques differ vastly in respect to the sample and its specific qualities to be observed as well as the specific microscope used. Details can be found in the relevant main articles listed above.

== Disadvantages ==
[[File:Jeol_Transmission_and_scanning_EM.jpg|right|thumb|[[JEOL]] transmission and scanning electron microscope made in the mid-1970s]]
Electron microscopes are expensive to build and maintain. Microscopes designed to achieve high resolutions must be housed in stable buildings (sometimes underground) with special services such as magnetic field canceling systems and anti vibration mounts.<ref>{{cite journal |vauthors=Song YL, Lin HY, Manikandan S, Chang LM |date=March 2022 |title=A Magnetic Field Canceling System Design for Diminishing Electromagnetic Interference to Avoid Environmental Hazard |journal=International Journal of Environmental Research and Public Health |volume=19 |issue=6 |pages=3664 |doi=10.3390/ijerph19063664 |pmc=8954143 |pmid=35329350 |doi-access=free}}</ref>

The samples largely have to be viewed in [[vacuum]], as the molecules that make up air would scatter the electrons. An exception is [[Liquid-Phase Electron Microscopy|liquid-phase electron microscopy]]<ref>{{cite journal |vauthors=Williamson MJ, Tromp RM, Vereecken PM, Hull R, Ross FM |date=August 2003 |title=Dynamic microscopy of nanoscale cluster growth at the solid-liquid interface |journal=Nature Materials |volume=2 |issue=8 |pages=532–536 |bibcode=2003NatMa...2..532W |doi=10.1038/nmat944 |pmid=12872162}}</ref> using either a closed liquid cell or an environmental chamber, for example, in the [[environmental scanning electron microscope]], which allows hydrated samples to be viewed in a low-pressure (up to {{convert|20|Torr|kPa|lk=in|abbr=on|disp=or}}) wet environment. Various techniques for [[in situ electron microscopy]] of gaseous samples have also been developed.<ref>{{cite journal |vauthors=Gai PL, Boyes ED |date=March 2009 |title=Advances in atomic resolution in situ environmental transmission electron microscopy and 1A aberration corrected in situ electron microscopy |journal=Microscopy Research and Technique |volume=72 |issue=3 |pages=153–164 |arxiv=1705.05754 |doi=10.1002/jemt.20668 |pmid=19140163}}</ref>
[[File:705_2020_4689_Fig2A.jpg|thumb|Pleolipoviral virion (HRPV-6)<ref>{{Cite journal |last1=Demina |first1=Tatiana A. |last2=Oksanen |first2=Hanna M. |date=2020-11-01 |title=Pleomorphic archaeal viruses: the family Pleolipoviridae is expanding by seven new species |journal=Archives of Virology |language=en |volume=165 |issue=11 |pages=2723–2731 |doi=10.1007/s00705-020-04689-1 |issn=1432-8798 |pmc=7547991 |pmid=32583077}}</ref>]]
Samples of hydrated materials, including almost all biological specimens, have to be prepared in various ways to stabilize them, reduce their thickness (ultrathin sectioning) and increase their electron optical contrast (staining). These processes may result in [[Visual artifact#In microscopy|artifacts]], but these can usually be identified by comparing the results obtained by using radically different specimen preparation methods. Since the 1980s, analysis of [[Cryofixation|cryofixed]], vitrified specimens has also become increasingly used.<ref name="Adrian-1984">{{cite journal |vauthors=Adrian M, Dubochet J, Lepault J, McDowall AW |year=1984 |title=Cryo-electron microscopy of viruses |url=https://serval.unil.ch/resource/serval:BIB_BEC796503260.P001/REF.pdf |journal=Nature |type=Submitted manuscript |volume=308 |issue=5954 |pages=32–36 |bibcode=1984Natur.308...32A |doi=10.1038/308032a0 |pmid=6322001}}</ref><ref name="Sabanay-1991">{{cite journal |vauthors=Sabanay I, Arad T, Weiner S, Geiger B |date=September 1991 |title=Study of vitrified, unstained frozen tissue sections by cryoimmunoelectron microscopy |journal=Journal of Cell Science |volume=100 |issue=1 |pages=227–236 |doi=10.1242/jcs.100.1.227 |pmid=1795028}}</ref><ref>{{cite journal |vauthors=Kasas S, Dumas G, Dietler G, Catsicas S, Adrian M |date=July 2003 |title=Vitrification of cryoelectron microscopy specimens revealed by high-speed photographic imaging |journal=Journal of Microscopy |volume=211 |issue=Pt 1 |pages=48–53 |doi=10.1046/j.1365-2818.2003.01193.x |pmid=12839550}}</ref>

Many samples suffer from [[radiation damage]] which can change internal structures. This can be due to either or both [[Radiolysis|radiolytic]] processes or ballistic, for instance with [[Collision cascade|collision cascades]].<ref>{{Cite journal |last1=Egerton |first1=R. F. |last2=Li |first2=P. |last3=Malac |first3=M. |date=2004-08-01 |title=Radiation damage in the TEM and SEM |url=https://linkinghub.elsevier.com/retrieve/pii/S0968432804000381 |journal=Micron |series=International Wuhan Symposium on Advanced Electron Microscopy |volume=35 |issue=6 |pages=399–409 |doi=10.1016/j.micron.2004.02.003 |issn=0968-4328|url-access=subscription }}</ref> This can be a severe issue for biological samples,<ref>{{Cite journal |last=Glaeser |first=Robert M. |date=1971-08-01 |title=Limitations to significant information in biological electron microscopy as a result of radiation damage |url=https://linkinghub.elsevier.com/retrieve/pii/S0022532071801181 |journal=Journal of Ultrastructure Research |volume=36 |issue=3 |pages=466–482 |doi=10.1016/S0022-5320(71)80118-1 |issn=0022-5320|url-access=subscription }}</ref><ref>{{Citation |last1=Baker |first1=Lindsay A. |title=Chapter Fifteen - Radiation Damage in Electron Cryomicroscopy |date=2010-01-01 |work=Methods in Enzymology |volume=481 |pages=371–388 |editor-last=Jensen |editor-first=Grant J. |url=https://linkinghub.elsevier.com/retrieve/pii/S0076687910810158 |access-date=2025-05-15 |series=Cryo-EM Part A Sample Preparation and Data Collection |publisher=Academic Press |doi=10.1016/s0076-6879(10)81015-8 |last2=Rubinstein |first2=John L.|url-access=subscription }}</ref>

== See also ==
{{div col|colwidth=20em}}
* [[List of materials analysis methods]]
* [[Electron diffraction]]
* [[Electron energy loss spectroscopy]] (EELS)
* [[:Category:Electron microscope images|Electron microscope images]]
* [[Energy filtered transmission electron microscopy]] (EFTEM)
* [[Environmental scanning electron microscope]] (ESEM)
* [[Immune electron microscopy]]
* [[In situ electron microscopy]]
* [[Low-energy electron microscopy]]
* [[Microscope image processing]]
* [[Microscopy]]
* [[Scanning confocal electron microscopy]]
* [[Scanning electron microscope]] (SEM)
* [[Thin section]]
* [[Transmission Electron Aberration-Corrected Microscope]]
* [[Volumetric Electron Microscopy]]
{{div col end}}

== References ==
{{reflist|30em}}

== External links ==
{{Library resources box
 |onlinebooks=no
 |by=no
 |lcheading=Electron microscopy
 |label=Electron microscopy}}
{{Commons category|Electron microscopes}}
* [http://www.fei.com/resources/student-learning/introduction-to-electron-microscopy/resources.aspx An Introduction to  Microscopy] {{Webarchive|url=https://web.archive.org/web/20130719110234/http://www.fei.com/resources/student-learning/introduction-to-electron-microscopy/resources.aspx |date=2013-07-19 }}: resources for teachers and students
* [https://library.ucsd.edu/dc/collection/bb5940732k Cell Centered Database – Electron microscopy data]
* [http://scienceaid.co.uk/biology/cell/analysingcells.html Science Aid: Electron Microscopy]:By Kaden park

{{Electron microscopy}}{{Authority control}}

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