How does it work? - Electron microscope

How does it work? - Electron microscope

This animation demonstrates the structure and operation of electron microscopes.



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Electron microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The resolution of a microscope limits its magnifying capacity. For optical microscopes the limit of resolution is about 0.2 microns. This means that it is impossible to differentiate two objects closer to each other than 0.2 microns.
As the wavelength decreases, the resolution increases. The wavelength of visible light is between 0.4 and 0.8 nanometers. Electron microscopes use electron beams, with a wavelength much smaller than that of visible light. Therefore, at 0.2 nm, they are capable of about a thousand times better resolution. This distance is not much more than the diameter of a hydrogen atom, thus electron microscopes can even be used to see small molecules. The first electron microscope was built by Ernst Ruska and Max Knoll in 1931.

Scanning electron microscope

Scanning electron microscopes create 3D images of the surface of the samples. The electron beam scans the surface of the sample via the deflection coil.
The electrons reaching the surface may be reflected or may cause the emission of secondary electrons. The quantity of these depends on the angle of the electron beam and the surface. The detector measures the quantity of reflected and secondary electrons. The image is created from these data by a computer.

Transmission electron microscope

In electron microscopes an electron gun emits an electron beam, which is focused on the subject by electromagnetic lenses. In transmission electron microscopes the beam passes through the thin sample and creates an image using electromagnetic lenses. The sample is stained by heavy metal salts: different parts of the sample bind the heavy metal ions to different extents. Heavy metal ions scatter electron beams and therefore they cause dark areas on the image.



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