electron microscope

The scanning electron microscope. Electrons from the electron gun are focused to a fine point on the specimen surface by the lens systems. The beam is moved across the specimen by the scan coils. Secondary electrons are emitted by the specimen surface and pass through the detector, which produces an electrical signal. The signal is passed to an electronic console, and produces an image on a screen.

A false-colour electron micrograph of the chickenpox virus Varicella zoster. Viruses are minute infectious particles that can only multiply if they invade a living cell and use its genetic machinery. It is therefore difficult to find a treatment that attacks the virus itself but leaves the host cell unharmed. A healthy body produces antiviral proteins to prevent the infection from spreading to adjacent cells. Though highly contagious, chickenpox usually creates a lifelong immunity. The chickenpox virus is part of the herpes family of viruses.

A scientist at work with an electron microscope, in a ‘clean room’ (an area set aside in a laboratory or research establishment where there is need for an absolutely clean, dust-free, and controlled environment). The electron microscope produces a greater magnification with much better resolution (definition) than an optical 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. See also atomic force microscope.

In 2004 the smallest image resolution ever achieved, of 0.06 nanometre (0.06 billionths of a metre), was reported by scientists of the Electron Microscopy Group of the Oak Ridge National Laboratory in Tennessee. They were able to image individual columns of atoms in a silicon crystal.