Centralized Resource Laboratory

Electron Microscopy

Electron Microscopes are scientific instruments that use a beam of highly energetic electrons to examine material objects on a very fine scale. This examination can yield the surface features of the objects, the shape and size of the particles making up the object at very high magnification and resolution. Also the defect and the other microstructures can be done on such microscopes. The elemental composition of the exposed samples can be studied by an attachment Energy Dispersive X-ray Analysis (EDX) with such equipment. Further, the distribution of different elements throughout the sample can be achieved.
Electron Microscopes were developed due to the limitations of Light Microscopes, which are limited by the physics of light to 500X or 1000X magnification and a resolution of 0.2 micrometers. In the early 1930's this theoretical limit had been reached and there was a scientific desire to see the fine details of the interior structures of organic cells that are nucleus, mitochondria...etc. This requires 10,000X plus magnification, which was impossible using optical Microscopes.
The Transmission Electron Microscope (TEM) was the first type of Electron Microscope to be developed and is patterned exactly on the Light Transmission Microscope except that a focused beam of electrons and electromagnetic lenses are used instead of light and optical lenses respectively to see through the specimen. Max Knoll and Ernst Ruska in Germany developed TEM in 1931. The first Scanning Electron Microscope (SEM) presented in 1932 while the first commercial instrument in 1965. Its late development was due to the electronics involved in scanning the beam of electrons on the sample.
Electron Microscopes (EMs) function exactly as optical microscopes, except that they use a focused beam of electrons instead of light to get image of the specimen and gain information of its structure and composition.
In all electron microscopes, a stream of electrons is produced by the Electron Source that is electron gun and accelerated toward the specimen using a positive electrical potential. This stream is focused, by using the metal apertures and the magnetic lenses into a thin, focused, monochromatic beam. Interactions occur between the irradiated sample and electron beam producing new signals affecting the path of the electron beam.  These interactions and effects are detected by different detectors and transformed into an image. These steps are carried out in all electron microscopes regardless of their type.

The main types of the electron microscopes are

  • Transmission Electron Microscope
  • Scanning Electron Microscopes