What is Electron Microscopy?

What is Electron Microscopy? Examples, Principles, and Types

There's more to this world than meets the eye... Literally!  

Invisible to the human eye and waiting to be discovered, there are so many complex hidden structures. Fortunately, with the power of electron microscopy, scientists and engineers can see into them and reveal their secrets.  

Electron microscopy (EM) has been at the forefront of high-resolution cellular imaging for over 50 years, thanks to its ability to examine nanometer-scale intracellular structures. From manifold bacteria to complex structures of materials, electron microscopy allows us to unravel all the mysteries.  

What is Electron Microscopy? 

Electron microscopy is a technique that allows obtaining high-resolution images of biological and non-biological specimens. It can be used in biomedical research to examine the detailed structure of tissues, cells, organelles and macromolecular complexes.  

The high resolution of EM images results from the use of electrons as the illuminating radiation. The wavelength of an electron is up to 100,000 times shorter than that of photons in the visible range, which allows electron microscopes to have a higher resolving power than optical microscopes and reveal structures of much smaller objects.  

Electron microscopy is used in conjunction with a variety of ancillary techniques, such as thin sectioning, immuno-labelling, negative staining or spectroscopic techniques to answer specific questions and respond to different challenges of modern laboratories and research facilities.  

Applications of Electron microscope  

The range of possible applications of electron microscopy is truly impressive. The ability to view the structure of a specimen at many times higher resolution than what is possible with optical microscopy gives it a distinct role in scientific research and industry requests.  

An electron microscope can be used to investigate the ultrastructure of a wide range of biological and inorganic specimens, such as microorganisms, cells, large molecules, biopsy samples, inorganic materials and crystal structures. It gives us a glimpse into the unknown world and helps us discover new properties and applications of various matters.  

Electron microscopy is also commonly used in research laboratories, universities, and nanotechnology centres. In these institutions, the structure of specimens can be observed in great detail to provide information about their function. It also supports biology and life sciences in areas such as toxicology, virology (e.g. viral load monitoring), drug research and electron tomography.  

Electron microscopy is also often used for industrial purposes to assist in developing new products, throughout the manufacturing process and to ensure the safety of processes across different industries, including mining, forensics, food science and fractography.  

Working Principle of Electron Microscopy 

Electron microscopes use signals from the interaction of an electron beam with the sample to obtain information about structure, morphology, and composition.  

There are some basic steps involved in all EMs:  

  1. A stream of high voltage electrons (usually 5-100 KeV) is emitted by the Electron Source (usually a heated tungsten or field emission filament) and accelerated in a vacuum toward the specimen using electric potentials.  
  2. This stream is confined into a thin, monochromatic, focused electron beam using electromagnetic lenses.  
  3. This electron beam is directed onto the sample using magnetic lenses.  
  4. Interactions occur with the irradiated sample, affecting the primary electron beam and generating products such as secondary electrons or characteristic X-rays.
  5. Products of these interactions are detected and transformed into an image.  

As simple as that! 

Types of electron microscopes  

We can distinguish two main types of electron microscopes that use different techniques to obtain an image. 

Scanning Electron Microscope (SEM)  

A scanning electron microscope produces images of a sample by scanning the surface with a focused beam of electrons. How exactly does it work? The electron beam interacts with atoms in the sample and produces various signals containing information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image.  

Because of its great depth of focus, a scanning electron microscope is the EM analogue of a stereo light microscope.  

Transmission Electron Microscope (TEM)  

Transmission Electron Microscope uses a beam of electrons transmitted through an ultrathin specimen to form an image. An image is formed as a result of the interaction of the electron beam with the sample as the beam goes through the specimen. Using similar optics geometry as in light microscopes the image gets magnified and focused on a series of detectors. 

A transmission electron microscope can capture incredible details - even crystal structures with atomic resolution, which is thousands of times smaller than objects visible through a light microscope. 

Transmission electron microscopy can be used across different areas, such as the physical, chemical and biological sciences. TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, semiconductor research, and even palaeontology and palynology. 

And there's more! Transmission Electron Microscopes can be used in scanning mode (STEM - Scanning Transmission Electron Microscope), combining both techniques’ advantages. 

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