Scanning tunneling microscope：Scanning tunneling microscope (STM)

scanning tunneling microscope (STM), type of microscope[1] whose principle of operation is based on the quantum[2] mechanical phenomenon[3] known as tunneling[4], in which the wavelike properties of electrons[5] permit them to “tunnel” beyond the surface of a solid into regions of space that are forbidden to them under the rules of classical physics[6]. The probability of finding such tunneling electrons decreases exponentially as the distance from the surface increases. The STM makes use of this extreme sensitivity to distance. The sharp tip of a tungsten[7] needle is positioned a few angstroms from the sample surface. A small voltage is applied between the probe[8] tip and the surface, causing electrons to tunnel across the gap. As the probe is scanned over the surface, it registers variations in the tunneling current, and this information can be processed to provide a topographical image of the surface.

The STM appeared in 19...