A Scanning Tunneling Microscope; a microscope that uses the phenomenon of quantum tunneling to map the electron surface of a material. Particularly useful if you want to "see" the configuration of a material's surface or do cool things like manipulate individual atoms. The classic examples are the quantum corral and the smallest IBM logo in the world. See also: Scanning Tunneling Microscopy, AFM (Atomic Force Microscope), SEM (Scanning Electron Microscope), LEED (Low Energy Electron Diffraction).