TRANSMISSION ELECTRON MICROSCOPE (TEM) - Working Principle and Applications

 TRANSMISSION ELECTRON MICROSCOPE

·       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 is used instead of light to "see through" the specimen.

·       TEM was developed by Max Knoll and Ernst Ruska in Germany in 1931.

Working Principle

·       Transmission Electron Microscope (TEM) requires vacuum system, consisting of pumps and their associated gauges and valves, and power supplies are required.

·       The Specimen (Sample) to be examined is made extremely thinner than those used in the Optical light microscope and Scanning Electron Microscope. Ultra-thin sections of 20 - 100 nm are cut which is already placed on the specimen holder.

·       In Transmission Electron Microscope (TEM), a finely focused beam of Electrons from an Electron gun passes to a specially prepared, Ultrathin section of the Specimen through Electromagnetic Condenser.

·       TEM use two Electromagnetic condenser lenses to control illumination, focus, and magnification.

·       The First Electromagnetic Condenser lens largely determines the "spot size"; the general size range of the final spot that strikes the sample. The Second Electromagnetic Condenser lens changes the size of the spot on the sample, changing it from a wide dispersed spot to a pinpoint beam.

·       The Specimen (Sample) is usually placed on a Copper mesh grid.

·       The beam of Electrons passes through the Specimen and then through an Electromagnetic Objective lens, which magnifies the image.

·       The Objective aperture enhance the contrast of the image by blocking out high-angle diffracted electrons.

·       Selected Area Aperture enabling the user to examine the periodic diffraction of electrons by ordered arrangements of atoms in the sample.

·       The image is passed down the column through the Intermediate and Projector Lenses, being enlarged all the way.

·       Finally, the electrons are focused onto a Fluorescent screen or Photographic plate. The final image is called a Transmission electron micrograph.

Uses

·       TEM is used to show the multiple characteristics of objects such as Ultrastructure of cell, Crystallization, Viruses and Tissues (usually magnified 10,000 – 1,00,000 X).

·       TEM is ideal for a number of different fields such as Life sciences, Nanotechnology, Medical, Biological & Material research, Forensic analysis and Metallurgy as well as industry and education.

·       TEM provides topographical, morphological, compositional and crystalline information.