Electron microscope

An electron microscope uses a beam of electrons to examine structures too small for conventional optical microscopy to resolve. Electrons have wave properties, and their wavelength at the energies used in these instruments is much shorter than that of visible light. Electron microscopy can therefore distinguish fine detail that an optical microscope cannot.

Principles

An electron source supplies a beam that is accelerated and controlled by electromagnetic lenses. Conventional instruments operate with the beam travelling through a vacuum. The resulting image depends on how electrons interact with the specimen and on which signals the instrument records.

Magnification and resolution are different properties. Enlarging an image does not by itself reveal additional detail: resolution is the ability to distinguish nearby features as separate. Electron microscopy extends the range of structures that can be resolved, making it useful in the study of cells and their internal organisation.

Main forms

In transmission electron microscopy, electrons pass through a sufficiently thin specimen. Differences in transmission reveal internal structure. In a scanning electron microscope, a focused beam moves across the specimen and signals from its interactions are used to construct an image, commonly emphasising surface detail.

Specimens

Conventional biological electron microscopy requires preparation suited to the instrument, including treatments that make the specimen compatible with examination under vacuum. Such preparations generally cannot be used to observe an intact living cell carrying out its normal activities. The choice between light and electron microscopy therefore depends on the question as well as on the size of the features of interest.

Attribution

Adapted with reference to English Wikipedia, revision 1380641101 (contributors and history), under CC BY-SA 4.0. The prose has been rewritten and checked against the cited sources; changes have been made.