Editing Electron microscope (section)

=== 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}}
[[File:Bacillus subtilis image.jpg|thumb|Image of ''[[Bacillus subtilis]]'' taken with a 1960s electron microscope]]
The 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 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 which provide signals carrying information about the properties of the specimen surface, such as its topography and composition. The image displayed by SEM represents the varying intensity of any of these signals into the image in a position corresponding to the position of the beam on the specimen when the signal was generated.<ref name=":0" />{{RP|pages=1-15}}

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>