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It is used to obtain images of conductive surfaces at an atomic scale ~2 Å (2 x 10-10 m). It can also be used to alter the observed material by manipulating individual atoms, triggering chemical reactions, and creating ions by removing individual electrons from atoms and then reverting them to atoms by replacing the electrons.
The STM is a non-optical microscope which employs principles of quantum mechanics. A very 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) or jump 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.
The STM is not the first machine to incorporate the concept of scanning a sample with a stylus. However, systems involving contact between the stylus tip and the material have issues with resolution, and damage to the tip and the sample. It was realised by the American physicist Russel Young at the National Bureau of Standards in the USA that one solution to this problem would be to maintain the stylus at a small, constant distance from the surface. He used the phenomenon known as field emission. If a sufficiently high potential is applied between stylus and surface, a current flows with a strength depending on the stylus-surface distance. If regulated by a servomechanism controlled by the current, this distance can be kept constant without mechanical contact. Young succeeded in building an instrument that worked on this principle. The distance between the stylus tip and the surface was approximately 200 Å. Its resolution was considerably poorer than that of an electron microscope.
However, Young realised that it should be possible to achieve better resolution by using the so-called tunnel effect. This is a quantum mechanics effect that allows an electron (and also other particles) to cross an area where, according to classical physics, it cannot exist since it has insufficient energy. It makes its way through a potential mountain by quantum-mechanical tunneling; hence the name tunneling microscope. This means here that if the tip of the stylus is near enough to the surface (10 Å, i.e. 1-2 atom diameters), a current flows even at low voltages. In the same way as field emission, it should be possible to control the stylus without mechanical contact. However, Young was unable to convert this idea into practice because of the exceptional experimental difficulties involved.
The first researchers to succeed in building a scanning tunneling microscope were Gerd Binnig and Heinrich Rohrer at the IBMThis article is about the International Business Machines Corporation; see IBM (disambiguation) for other uses of this abbreviation. International Business Machines Corporation IBM or colloquially, Big Blue (incorporated June 15, 1911, in operation since Research Laboratories in Zürich, Switzerland. The reason for their success was the exceptional precision of the mechanical design. One example of this is that disturbing vibrations from the environment were eliminated by building the microscope upon a heavy permanent magnet floating freely in a dish of superconducting lead. Less bulky but equally effective devices for stable, disturbance-free suspension of the microscope have since been developed. Piezoelectrical elements are used to control the horizontal movement of the stylus in two perpendicular directions so that it scans the surface along parallel lines - hence the name scanning microscope. The vertical movement of the stylus is controlled and measured using another piezoelement. Using a special technique it has been possible to produce styluses with tips consisting of a single atom. Consequently, the image is particularly precise. Horizontal resolution is approximately 2 Å, and vertical resolution approximately 0.1 Å. This makes it possible to depict individual atoms, that is, to study in the greatest possible detail the atomic structure of the surface being examined.
Gerd Binnig and Heinrich Rohrer shared half of the Nobel PrizeThe Nobel Prizes (pronounced no-BELL or no-bell are awarded annually to people who have done outstanding research, invented groundbreaking techniques or equipment, or made outstanding contributions to society. It is generally regarded as the supreme comme in physics in 1986 for their achievement. The other half went to Ernst RuskaErnst August Friedrich Ruska ( December 25, 1906 May 25, 1988) was a German physicist. Ruska was born in Heidelberg. He was educated at the Technical University of Munich from 1925 to 1927 and then entered the Technical University of Berlin, where he posi for his fundamental work in electron optics, and for the design of the first electron microscope.* Sourced from the 1986 Nobel Prize in Physics Press Release - Copyright owner (Nobel Foundation) allows publishing without permission according to copyright statement