Electron Microscopy.

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Electron Microscopy.

Electron microscopy is a method of imaging that uses an electron microscope to enlarge small specimens by a greater magnification and resolution than conventional light microscopes. The photographs produced of specimens viewed with an electron microscope are call electronmicrographs. Magnification is the increase in apparent size of the specimen and resolution (also called resolving power) is the ability of the microscope to distinguish and produce separate images of closely placed objects. These two primary properties of electron microscopes make them extremely useful in the analysis and study of specimens.

The obvious difference between electron microscopes and light microscopes is the medium through which each operates. Light microscopes work by using photons to produce an image whereas electron microscopes use electrons to produce an image. The magnifying power of a light microscope is limited by the wavelength of visible light so electrons are used instead because they have a much smaller wavelength so can therefore resolve much smaller structures. The resolving power of a microscope depends on the wavelength of the electromagnetic radiation used. However, the benefits gained by using an electron microscope also bring specific problems that have to be tackled.
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Electron beams cannot pass through glass because electrons are physical matter. Therefore there cannot be any lenses used to focus the electrons like there are with optical microscopes. Instead the microscope uses electromagnets to focus the image onto a fluorescent screen. Another problem is that the electrons are very easily interrupted and scattered by molecules in the air so their path is distorted. To overcome this there has to be a very high vacuum inside the microscope so that there is the absence of any other particles in the path of the electron beams. Consequently electron microscopes can ...

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