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An electron microprobe is a versatile instrument that bombards a small sample with a beam of high- energy electrons. Specimens usually are polished (especially for quantitative analysis) and must be coated with a thin film of carbon or metal to prevent the buildup of an electrical charge. This electron beam excites the specimen to produce physical effects that can be used to extract various types of microscale information (see details below). These effects range from atomic density (indicated by an effect known as “backscattered electrons”) to elemental abundance. The concentration of an element can be shown in a map of the specimen or can be quantified by comparison to standards with known amounts of the element. For quantitative analysis, the excited area of the specimen can be as small as about 2 microns in diameter; a micron is 1/1000 of a millimeter. Thus, very small areas can be analyzed chemically and those areas can be linked to the distribution of elements throughout the specimen. This detailed information can be applied to science and engineering fields as diverse as geology, archeology, materials science, metallurgy, chemistry, physics, gemology, electronics, biology, medicine, dentistry, environmental science and engineering, and forensics, to name a few.

The microprobe also can function fully as an SEM, with most of the imaging capabilities thereof. Although the Yale JEOL 8600 lab concentrates primarily on quantitative microscale chemical analysis, secondary and backscattered electron imaging play an important role in evaluating the textural relationships of analyzed areas. In addition, some of the research in the lab uses primarily the SEM imaging capabilities. More details on the theory of electron imaging, including comparisons to resolution by optical and TEM analysis, should be available elsewhere. Unfortunately, the reference pages we had linked previously seem to have disappeared…

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