tunnelling (rus. туннелирование) — a tunnel effect occurring, when a particle, originally localisised by the one side of the potential barrier (the field which a classical particle cannot cross because the potential energy exceeds its total energy) can enter through the barrier with the probability other than zero and be detected by the other side of the barrier.

Description

Tunnelling probability decreases to a great extent as the height and width of the potential barrier increases, so this effect is most pronounced if the object size goes down 1-5 nm. The tunnel effect is a purely quantum phenomenon, which has no classical analogue: it underlies many important phenomena in atomic and nuclear physics, in particular, the alpha decay of radioactive nuclei. As a result of the combined effects of short-range nuclear forces of attraction and electrostatic (Coulomb) forces of repulsion, an alpha particle, when it exits from the nucleus, has to overcome a three-dimensional potential barrier of the type described above. Thermonuclear reactions would not be possible without the tunnelling effect: the Coulomb potential barrier that prevents the reagent nuclei from approaching as required for the synthesis is overcome partly due to high speeds (high temperatures) of the nuclei, and partly due to the tunnel effect.

The examples of the tunnel effect are especially numerous in solid state physics: field-emission of electrons from metals and semiconductors (tunnelling emission); tunnelling of charge carriers through the p-n junction potential barrier, which found practical application in the diodes; the migration of the valence electrons in the crystalline lattice; the effects arising at the contact between two superconductors with a thin dielectric film between them (the Josephson effect). The role of tunnel effects is exceptionally large in chemical processes at low and cryogenic temperatures (see cryochemistry); the effects arising at the contact between two superconductors with a thin dielectric film between them (the Josephson effect).

Authors

  • Khokhlov Dmitry R.
  • Shlyakhtin Oleg A.

Sources

  1. Physical Encyclopedic Dictionary (in Russian). — // Moscow: The Great Soviet Encyclopedia, 1995. — 928 pp.
  2. The Great Soviet Encyclopedia. — Мoscow: Sovetskaja ehnciklopedija, 1969–1978.
  3. V.I. Goldansky, L.I. Trahtenberg and V.N. Flerov, Tunneling Phenomena in Chemical Physics (in Russian) // Moscow: Nauka, 1986. — 296 pp.

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