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Scanning Electron Microscope

JEOL Environmental SEM with Oxford EDX

The Scanning Electron Microscope (SEM) is the premiere instrument in the generation of topographical images due to its unbelievable resolution.  Resolution is the ability to discern one point from another, and the diffraction of light is the limiting factor of resolution in microscopy.  With a typical light microscope, visible light has wavelengths from 4,000 to 7,000 Angstroms and the resolution is limited to about 1000 diameters magnification.  In contrast, the SEM uses light with a wavelength of 0.12 Angstroms, lending to this instrument a limit of resolution of 1 million diameters magnification.

The SEM's principle component is a focused beam of electrons passing through a vacuum and making contact with a solid of interest.  Those electrons bombard the sample and are released as secondary electrons.  The SEM's primary imaging method is through the collection of those secondary electrons (or backscattered electrons) that are released by the sample. These backscattered electrons are detected by a scintillation material, which is a radiation detector that produces flashes of light from the electrons. The light flashes are then detected and amplified by a photomultiplier tube.

The SEM does not only allow for excellent micrographs to be generated, the x-ray analyzer matches an element to its signature peaks, leading to its proper identification.  This analyzer has a beryllium filter on it, meaning that anything smaller than Be will not be effectively identified.  The x-ray analyzer is of great use when looking at an imperfection at the elemental level.  If the imperfect sample of interest is a manufactured product, this could be the first step in finding the problem.  This could then be followed by sampling the assembly line and determining exactly where the imperfection was introduced.

The instruction booklet instructs the scientist on the proper use of Marshall's scanning electron microscope (saved as a pdf format).
Contact Information
Dr. Michael L. Norton 
Marshall University Dept. of Chemistry


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