Scanning electron microscopy

In 1934, M. von Ardenne proposed that a finely demagnified electron beam could be scanned in a series of fine lines (a raster) over a specimen, and an electronic signal obtained that would reveal the amount of electrons reflected from the surface, or the amount of excited (secondary) electrons generated from within the specimen. It was more than 20 years later when T. Everhardt and R. Thornley, two students at Cambridge University in England, developed a working electron detection system that made the instrument practical. The first commercial scanning electron microscope was developed in England in 1965.

A key component of the scanning electron microscope is an electronic detector positioned near the specimen that captures secondary electrons from the specimen. The detector converts the signal to photons of visible light which in turn were used to drive a signal within a photo-multiplier tube that regulates the intensity of a corresponding electron beam on a display cathode ray tube (or monitor). The same basic system is still used in modern instruments as shown here.

Scanning electron microscopy reveals details of surface structure, as opposed to the two-dimensional sectional views normally presented with the aid of the transmission electron microscope. Some instruments, such as the one shown here, are also capable of viewing specimens with only a partial vacuum and can regulate water content and temperature.