Electron Microscopes

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  • Electron Microscopes
    • The Uses of Electrons
      • They generate a beam of electrons which have a wavelength 100,000x shorter than light.
      • They use magnets instead of lenses to focus the beam of electrons.
      • Electrons are not visible to the human eye so the image produced is projected onto a screen to make a black and white image. (greyscale image)
        • images are called electron micrographs
      • Resolution of the electrons is around 500,000x greater than that or a human eye.
    • Transmission Electron Microscopes (TEM)
      • The electron beam passes through a very thinly prepared sample
        • Electrons pass through the denser parts of the sample more easily which gives the micrograph contrast.
      • The final image produced is 2D
      • The magnification possible with a TEM is 500,000x
    • Scanning Electron Microscopes (SEM)
      • The electron beam is directed onto a sample and the electrons don't pass through the specimen.
        • Electrons are 'bounced off' the sample
      • the final image produced is 3D
      • The magnification possible with an SEM is 100,000x
    • Coloured Electron Micrographs
      • Electron micrographs are sometimes shown in colour because colour has been added to show different components.
        • 'False-Colour' micrographs.
      • All original micrographs are greyscale/ black and white images.
    • Disadvantages
      • Samples have to be placed in a vacuum
      • Electron microscopes are extremely expensive.
      • Preparing samples requires a high degree of skills and training.

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