Electron microscopy/function

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Electron Microscopy-Function

In contrast with the light microscope, the electron microscope uses na electron beam that interfere with the specimen ( biological or inorganic ) placed in the tube. They are frequently used to examine cells, microorganisms, metals, crystals and biopsy samples. This type of microscope can reveal a wide variety of information about a specimen including morphology, crystallographic information, compositional information and topography. Electron microscopes are valuable tools in medical and biological fields, as well as in the industry for materials research. Almost all scientific fields can use electron microscopes. The most common fields of study are biology, medicine, chemistry and forensics.

:Transmission Electron Microscope

The transmission electron microscope (TEM) uses a high voltage beam of electrons to create an image of a specimen. The electrons emitted by an electron gun are accelerated, focused and transmitted through a partially transparent specimen. The beam then emerges from the specimen and carries information to the objective lens where magnification occurs. Photographic recording of the image can also occur by exposing film directly to the beam. TEMs can yield information about the morphology including size, shape and arrangement of particles. They can also relay crystallographic information for example the arrangement of atoms and their degree of order, compositional information ( relative ratios of the elements and compounds or defects in areas as small as a few nanometers) .

:Scanning Electron Microscope

Unlike the TEM, the scanning electron microscope (SEM) makes an image by using the electron beam that scans the specimen across a rectangular area. Known as raster scanning, the electron beam loses energy as it scans each point on the specimen. This lost energy is converted into heat, light and secondary electron emission. The display maps these varying intensities into an image relying on surface properties rather than transmission. While an SEM produces an image with a slightly lower resolution, it can analyze larger specimens and can produce great representations of 3D shapes. Like the TEM, a SEM can present information about morphology, composition and crystallography. However, they are limited to looking at composition in areas of one micrometer and degrees of order on single-crystal particles of greater than 20 micrometers. In addition, a SEM can also yield information about topography,the surface features and texture, down to a few nanometers.

:List of some applications

1. Biology/Medicine

• Diagnostic electron microscopy
• Cryobiology
• Protein localization
• Electron tomography
• Cryo-electron microscopy
• Toxicology
• Biological production and viral load monitoring
• Particle analysis

1. Industry

• Particle detection and characterization
• Direct beam-writing fabrication
• Dynamic materials experiments
• Sample preparation
• Forensics
• Mining (mineral liberation analysis)

References 1)William R. Herguth, President, Guy Nadeau.Applications of Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM/EDS) To Practical Tribology Problems. Senior Technical Associate Herguth Laboratories, Inc. 2)M.Von Heimendahl, W.Bell, G.Thomas. Applications of Kikuchi line . Analyses in Electron Microscopy. Journal of Applied Physics 35 (1964)