How do scanning electron microscopes work

How does an electron microscope work?

An electron microscope creates the enlarged image of an object / structure not with the help of light rays, but with electron beams. The reason is simple: the wavelength of light limits the resolution of a light microscope. With light or transmitted light microscopes, structures down to a minimum of around 200 nanometers (= one millionth of a millimeter) can be made visible.

Because of the much shorter wavelength of electron beams, structures down to a minimum length of 0.1 nanometers can be viewed with an electron microscope. This means that the resolution of an electron microscope is almost 1,000 times greater than that of a light microscope.

Scanning Electron Microscope (SEM)

With the scanning electron microscope, the image is enlarged with the help of electrostatic lenses, similar to the light microscope. A very fine electron beam is moved over the object in a grid pattern - it is, as it were, scanned. The German abbreviation is REM, but after the English "scanning electron microscope"it is usually referred to as SEM.


An electron beam is generated at the top of the electron microscope and fired downwards towards the object. Ring-shaped "amplifiers" in the high tube focus this beam, which is so super fine. If it falls on the object below, this point itself emits electrons which are caught by a detector. If the beam is directed at another point, other electrons are emitted and picked up by the detector. To generate an image of the object, the electron beam scans the object like a grid - and the detector uses this to compose the corresponding image.

With the help of the electrostatic lenses, she creates this grid very finely. The finer the grid, the higher the resolution. The following instructional video from the Bavarian broadcasting company once again explains very clearly how an electron microscope works.

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How an electron microscope works

Ernst Ruska and the electron microscope:

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Ernst Ruska and the electron microscope

Coronavirus under the electron microscope

Viruses are so small that you can hardly see them with a light microscope. But you can make them visible with an electron microscope. The following colored illustration shows some coronaviruses:

More on the subject of Coronavirus Sars-CoV-2 at

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