With the scanning electron microscope (SEM), scientists in a range of fields—from biology to materials science to microelectronics—can analyze the surface of objects with a resolution approaching molecular dimensions. Although conceptually developed in the 1940s, the SEM was not put into practical use until the 1960s. Improvements in SEM technology continue with the introduction this year of a device that can image unprepared specimens without contaminating the microscope or charging or degrading the specimen.

Secondary Electrons

Using a scanning electron beam of extremely small diameter, the SEM generates low-energy, secondary electrons in the upper 100 A of the specimen. These secondary electrons are bent and collected by a detection system that is scanned in synchronization with a cathode ray tube (CRT). The strength of the detected signal determines the CRT brightness, thereby producing an image of the specimen.

Specimen detail can be examined with a resolution as low as 20...

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