Electron Microscope | Working | 2 Important Types | Uses



What is electron microscopy?

Electron microscope (EM) refers to a method that allows analyzing and observation of very high-resolution images of various living and non-living samples. These types of microscopes are utilized for biomedical research in order to examine the detailed shape and structure of tissues, cells, organelles, and other macromolecular complexes. Electrons (that act as a source of illuminating radiation in this case) have very short wavelengths that help in producing a high resolution of electron microscopy images. Generally, electron microscopy is combined with a number of ancillary techniques such as immuno-labeling, thin sectioning, negative staining, etc. for examining certain specific structures. Electron microscopic images can provide important data on the structural basis of cell/tissue function and of cell disease.  

electron microscope
An early electron microscope. Image source: J Brew, uploaded on the English-speaking Wikipedia by en:User:Hat’nCoat., Ernst Ruska Electron Microscope – Deutsches Museum – Munich-editCC BY-SA 3.0

What are the types of electron microscopy?

Electron microscope can be of two different types:

Transmission Electron Microscope (TEM): Transmission Electron Microscope is used for viewing extremely thin specimens such as molecules, tissue sections, etc. In this, electrons can pass through such tissues to project an image. The TEM is similar to the typical compound light microscope in many ways. Like a compound microscope, TEM is used for imaging the interior of biological cells in extremely thin layers, the structure of protein molecules that is contrasted with the help of metal shadowing, the structural molecule-organization in cytoskeletal filaments by using the negative staining technique, and the structural protein molecule arrangement in cell membranes by using the freeze-fracture technique.

A modern transmission electron microscope. Image source; David J Morgan from Cambridge, UK, Electron MicroscopeCC BY-SA 2.0

Scanning Electron Microscope (SEM): Scanning Electron Microscope or SEM is dependent upon the emission of secondary electron from the upper layer of the specimen. Scanning Electron Microscopes can provide a great depth of focus due to which, it can be utilized as a stereo light microscope. This helps us to image extremely delicate and detailed structural and physical properties of cells, tissues, organelles, and other macromolecular complexes which cannot be performed with TEM. Scanning electron microscopes fids its applications in cell-counting, size-determination the sizes of macromolecular complexes, and process control.

The microscope design is named as Scanning electron microscope because this microscope generates images by scanning the surface of the sample by using an electron beam. The scattered surface emissions are then gathered by using detectors. SEMs can be further categorized into two types, scanning tunneling microscopy, and scanning transmission electron microscopy.

A scanning electron microscope. Image source: Dr Graham BeardsJeol Transmission and scanning EMCC BY-SA 4.0

How does an electron microscope work?

A demonstration of the resultant phenomenon after an excited electron beam interacts with a sample. Image source: Claudionico~commonswikiElectron Interaction with MatterCC BY-SA 4.0

The working of an electron microscope is similar to that of an optical microscope except for the fact that electron microscopy involves the use of electron beams for image formation instead of photons. A heated tungsten or field emission filament acts as a source of the electron beam and emits a stream of high voltage electrons of about 5-100 KeV. A positive electric potential further accelerates the electron beam in a vacuum. This stream of electrons is then focused into a thin monochromatic beam by using magnetic lenses. The focused beam falls on the sample specimen interacting with the material. these interaction patterns are observed and detected by the fluorescent screen and camera to form images.

What are the advantages of electron microscopy?

Electron microscopy has a set of advantages such as:

  • Electron microscopy helps to analyze and observe very high-resolution images of various living and non-living samples.
  • Electron microscopic images can provide important data on the structural basis of cell/tissue function and of cell disease that is not resolved by other types of microscopes properly.
  • Electron microscopy allows the imaging of extremely delicate biological structures without forcing any kind of damage on them.
  • Electron microscopy provides extremely accurate images if it is set-up properly.

What are the disadvantages of electron microscopy?

Electron microscopy has a set of disadvantages such as:

  • Building and maintaining the running and setup cost of the electron microscopes can be expensive.
  • These microscopes require to be placed in stable buildings with instruments to cancel magnetic fields in order to achieve high-resolution images.
  • The samples used in electron microscopy should be kept in a vacuum for avoiding the air molecules to scatter the electrons and interfere with the image formation.
  • These microscopes generally work with conductive specimens. So, non-conductive materials require a conductive coating of gold/palladium alloy, carbon, osmium, etc. for proper imaging.

What are the applications of an electron microscope?

Electron microscope can find its applications in various fields such as:

  1. Semiconductor and data storage: Electron microscopy is used widely in various semiconductor and data storage processes such as circuit edit, failure analysis, and defect analysis.
  2. Industry: Electron microscopy is used widely for a number of industrial work like direct beam-writing fabrication, micro-characterization, pharmaceutical QC, mining (mineral liberation analysis), fractography, food science research, forensic research, and chemical or petrochemical analysis.
  3. Biology and life sciences: Electron microscopy is used widely for a number of biological research work such as cryobiology, cryo-electron microscopy, drug research (e.g. antibiotics), diagnostic electron microscopy, virology (e.g. viral load monitoring), electron tomography, protein localization, particle analysis, structural biology, particle detection, tissue imaging, and toxicology.
  4. Materials research: Electron microscopy is used widely in various material research purposes such as dynamic materials experiments, device testing, and characterization, In-situ characterization, Electron beam-induced deposition, medical research, material qualification, Nanoprototyping, and Nanometrology.

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About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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