scanning tunnelling microscope

Microscope that produces a magnified image by moving a tiny tungsten probe across the surface of the specimen. The tip of the probe is so fine that it may consist of a single atom, and it moves so close to the specimen surface that electrons ‘tunnel’ (that is, jump) across the gap between the tip and the surface.

The magnitude of the electron flow (current) depends on the distance from the tip to the surface, and so by measuring the current, the contours of the surface can be determined. These can be used to form an image on a computer screen of the surface, with individual atoms resolved. Magnifications up to 100 million times are possible. The STM can also be used to manipulate, rather than image, individual atoms on the surface of a material.

The STM was invented in 1981 by Gerd Binning from Germany and Heinrich Rohrer from Switzerland at the IBM Zürich Research Laboratory. With Ernst Ruska, who invented the transmission electron microscope in 1933, they were awarded the Nobel Prize for Physics in 1986.