Microscopes, Electron, Scanning
Definition : Electron microscopes designed to provide a topographical image of the surface of a specimen, useful for understanding its surface structure. Scanning electron microscopes (SEMs) consist of an electron gun and vacuum chamber, an electromagnetic imaging (lens) system, a scanning system, a specimen chamber, secondary and backscatter detectors, a viewing chamber and fluorescent screen, and photographic and vacuum systems. The imaging system provides an electron beam with a fine focal spot that is deflected horizontally and vertically (i.e., scanning system); the energy exchange between the electron beam and the sample yields electromagnetic radiation that is detected to produce an image. Before observation, tissue samples must be fixed (including cryofixation for some dedicated instruments), processed, embedded, sectioned, mounted on a support stub, and usually coated (e.g., using a sputter coater) with a thin film of a heavy metal (e.g., gold). The clinical use of SEMs has yielded information on hematologic disorders and biological surfaces, such as those of the small intestines and serous cavities.
Entry Terms : "SEMs" , "Scanning Electron Microscopes"
UMDC code : 18089