Electron microscopy is used to examine specimens which require greater detail than can be seen when using the light microscope. In comparison to light microscopes electron microscopes provide a clearer picture, greater magnification and greater resolution. There are two types of electron microscope; the scanning electron microscope and the transmission electron microscope. Electron microscopes use electromagnetic and electrostatic lenses and some are able to magnify the specimen size by millions. The transmission electron microscope magnifies over 50,000,000X the resolution of a TEM is 0.
2nm. The TEM works by beaming electrons through the sample and this is detected on a florescent screen. The TEM is able to show the structure of specimens as the beams pass through the specimen rather than bouncing on it in the way a scanning microscope would, this is a reflection transmission electron microscope. The scanning electron microscope is able to produce a 3D image.
The resolution of an SEM is 10nm; this however is lower than that of a TEM, although still very high in comparison to a light microscope.
The magnification range for an SEM is generally 20x to 500,000X. An electron beam scans points of the specimen; this is reflected off the surface and then enhanced electronically In order to use an electron microscope to examine a specimen it must first be treated, there are several way of doing this including cryofixation, fixation, dehydration, embedding, sectioning, staining, freeze fracture and sputter coating. As well as the advantages of electron microscopy there are also disadvantages. Electron microscopes are not able to show colour, they are also very expensive to purchase and maintain, they are also large and not very portable.
Samples must be viewed in a vacuum as electrons are scattered if exposed to the air.
The treatments used to treat specimens before they are examined under an electron microscope can cause the specimen to become an artifact and this can destroy some of the sample. In addition the electron microscope is more complicated to use than the simpler light microscope. One of the biggest drawbacks of the electron microscope is the inability to view living specimens. The different types of electron microscope serve different purposes and each has its advantages and disadvantages as well as limitations Electron microscopes have enabled scientists to make discoveries and examine specimens which were previously inaccessible with light microscopes, they have great value in many fields including research and medicine.
Transmission Electron Microscope
Source – http://www.biologie.uni-hamburg.de/b-online/e03/03e.htm [accessed 23rd January 2013]
Scanning Electron Microscope
Source – http://www.jic.ac.uk/microscopy/intro_em.html [accessed 23rd January 2013]
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