electron microscope

Instrument that produces a magnified image by using a beam of electrons instead of light rays, as in an optical microscope. An electron lens is an arrangement of electromagnetic coils that control and focus the beam. Electrons are not visible to the eye, so instead of an eyepiece there is a fluorescent screen or a photographic plate on which the electrons form an image. The wavelength of the electron beam is much shorter than that of light, so much greater magnification and resolution (ability to distinguish detail) can be achieved. The development of the electron microscope has made possible the observation of very minute organisms, viruses, and even large molecules.

A transmission electron microscope passes the electron beam through a very thin slice of a specimen. A scanning electron microscope looks at the exterior of a specimen. A scanning transmission electron microscope (STEM) can produce a magnification of 90 million times.