Electron and Light microscopes

The differences between electron and light microscopes

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Light microscope drawbacks

  • Poor resolution because of the long wavelength of light.
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Electron microscope benefits/drawbacks

  • An electron beam has a short wavelength and therefore an electron microscope has a high resolving power.
  • Electrons have a negative charge. This means that the beam can be focused by using an electronmagnet.
  • Electrons are absorbed by molecules in the air.
  • A near vacuum has to be created to make the microscope work efficiently.
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TEM electron microscopes

  • TEM: Transmission Electron Microscope
  • A beam is passed through a thin section of the specimen.
  • Some parts absorb electrons so this appears dark, whereas other parts allow electrons to pass through and this appears bright.
  • The resolving power of a TEM is 0.1 nm which is very high.
  • Specimens must be very thin, and it is difficult to built up a 3D image.
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SEM electron microscopes

  • SEM: Scanning Electron Microscope.
  • Pass a beam back and forth through a specimen which can build up a 3D image.
  • Has a lower resolving power than a TEM; 20nm but this is still 10x better than a light microscope.
  • Specimens do not have to be as thin as in a TEM as the electrons do not penetrate.
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