what is scanning tunneling microscopy ?

Answer 1

Scanning Tunneling Microscopy, or STM is a non-optical method of microscopy which employs principles of quantum mechanics. An atomically sharp probe (the tip) is moved over the surface of the material under study, and a voltage is applied between probe and the surface. Depending on the voltage, electrons will "tunnel" (this is a quantum-mechanical effect) or jump from the tip to the surface (or vice-versa depending on the polarity), resulting in a weak electric current. The size of this current is exponentially dependent on the distance between probe and the surface. Obviously, for a current to occur the substrate being scanned must be conductive. Insulators cannot be scanned through STM.

STM (not to be confused with the scanning electron microscope) was invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM's Zurich Lab in Zurich, Switzerland. Although initially greeted with some scepticism by materials scientists, the invention garnered the two a Nobel Prize in Physics (1986). The STM allows scientists to visualize regions of high electron density and hence infer the position of individual atoms and molecules on the surface of a lattice. Previous methods required arduous study of diffraction patterns and required interpretation to obtain spatial lattice structures. The STM is capable of higher resolution than its somewhat newer cousin, the atomic force microscope (AFM). Both the STM and the AFM fall under the class of scanning probe microscopes.

The STM can obtain images of conductive surfaces at an atomic scale 2 × 10−10 m or 0.2 nanometer, and also can be used to manipulate individual atoms, trigger chemical reactions, or reversibly produce ions by removing or adding individual electrons from atoms or molecules.

Answer 2

STM. Let's start with the T. The "tunnelling" is quantum-mechanical leakage of the electrons from a material into the very fine tip of the STM probe. So the size of the signal is proportional to the tunneling matrix element. This can be tuned with applied voltage, so it's a local probe of the density of states.

S. "Scanning" because the tip can be moved over the surface of the object in question to m an image.

M. "Microscopy" because you are looking at things on a very small (basically atomic) resolution.

Answer 3

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