STM

A scanning tunneling microscope (STM) is used to obtain atomic-scale images of metal surfaces.

The STM is a high-resolution non-optical microscope which employs principles of quantum mechanics. A fine probe is moved over the surface of the material under study, and a voltage is applied between probe and the surface. Depending on the voltage and its characteristics electrons will "tunnel" (this is a quantum-mechanical effect) from the probe to the surface (or vice-versa depending on the polarity), resulting in a weak electric current. The size of this current is highly dependent on the distance between probe and the surface. By scanning the probe over the surface and measuring the current, one can thus reconstruct the surface structure of the material under study. Adjustments of the distance between probe and surface are done using a servo loop and converse piezoelectricity. It is even possible to move and position individual atoms, which makes the scanning tunneling microscope an important tool in nanotechnology.

The scanning tunneling microscope was developed at IBM Zürich in 1981 by Gerd Binnig and Heinrich Rohrer who shared half of the Nobel Prize in physics in 1986 for their achievement. The other half went to Ernst Ruska for his fundamental work in electron optics, and for the design of the first electron microscope.

See also: microscopy, electron microscope, atomic force microscope