Transmission Electron Microscope | TEM

Working Principles:
A transmission electron microscope fires a beam of electrons through a specimen to produce a magnified image of an object.
TEM working flows.
  1. A high-voltage electricity supply powers the cathode.
  2. The cathode is a heated filament, a bit like the electron gun in an old-fashioned cathode-ray tube (CRT) TV. It generates a beam of electrons that works in an analogous way to the beam of light in an optical microscope.
  3. An electromagnetic coil (the first lens) concentrates the electrons into a more powerful beam.
  4. Another electromagnetic coil (the second lens) focuses the beam onto a certain part of the specimen.
  5. The specimen sits on a copper grid in the middle of the main microscope tube. The beam passes through the specimen and "picks up" an image of it.
  6. The projector lens (the third lens) magnifies the image.
  7. The image becomes visible when the electron beam hits a fluorescent screen at the base of the machine. This is analogous to the phosphor screen at the front of an old-fashioned TV.
  8. The image can be viewed directly (through a viewing portal), through binoculars at the side, or on a TV monitor attached to an image intensifier (which makes weak images easier to see).
Applications:
  • Size of nanoparticles.
  • Morphology (structure) of samples.
  • Composition and some bonding states.
  • Growth of layers, their composition and defects in semiconductors.
  • Provides topographical, morphological, compositional and crystalline information.

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