scanning tunneling microscope

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scanning tunneling microscope

(STM), device for studying and imaging individual atoms on the surfaces of materials. The instrument was invented in the early 1980s by Gerd BinnigBinnig, Gerd
, 1947–, German physicist, Ph.D. Univ. of Frankfurt, 1978. At the IBM Research Laboratory in Zürich, Binnig and fellow researcher Heinrich Rohrer built the first scanning tunneling microscope, an instrument so sensitive that it can distinguish individual
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 and Heinrich RohrerRohrer, Heinrich,
1933–2013, Swiss physicist, Ph.D. Swiss Federal Institute of Technology, 1960. He joined IBM in 1963 and spent almost his entire career with the company, retiring in 1997.
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, who were awarded the 1986 Nobel prize in physics for their work. The underlying principle of the STM is the tunnelingtunneling,
quantum-mechanical effect by which a particle can penetrate a barrier into a region of space that would be forbidden by ordinary classical mechanics. Tunneling is a direct result of the wavelike properties of particles; the wave associated with a particle "decays"
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 of electrons between the sharp tip of a probe and the surface of the sample under study. The flow of electrons is extremely sensitive to the distance between the tip and the sample. As the tip is swept over the surface the height of the tip is continually adjusted so as to keep the flow of electrons constant. A map of the "bumps" on the surface is then obtained by accurately recording the height fluctuations of the tip. The STM was used in 2004 to measure the charges of individual atoms, and in 2010 researchers used a modified STM to observe the magnetism, or spin, of atoms on the nanosecond timescale.
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Scanning tunneling microscope

An instrument for producing surface images with atomic-scale lateral resolution, in which a fine probe tip is scanned over the surface at a distance of 0.5–1 nanometer, and the resulting tunneling current, or the position of the tip required to maintain a constant tunneling current, is monitored.

Scanning tunneling microscopes have pointed electrodes that are scanned over the surface of a conducting specimen, with help from a piezoelectric crystal whose dimensions can be altered electronically. They normally generate images by holding the current between the tip of the electrode and the specimen at some constant (set-point) value by using a piezoelectric crystal to adjust the distance between the tip and the specimen surface, while the tip is piezoelectrically scanned in a raster pattern over the region of specimen surface being imaged. By holding the force, rather than the electric current, between tip and specimen at a set-point value, atomic force microscopes similarly allow the exploration of nonconducting specimens. In either case, when the height of the tip is plotted as a function of its lateral position over the specimen, an image that looks very much like the surface topography results.

It is becoming increasingly possible to record other signals (such as lateral force, capacitance, scan-related tip displacement, temperature, light intensity, or magnetic resonance) as the tip scans. For example, modern atomic force microscopes can map lateral force and conductivity along with height, while image pairs from scanning tunneling microscopes scanning to and fro can provide information about friction as well as topography.

Scanning tunneling microscopes make it possible not just to view atoms but to push them and even to rearrange them in unlikely combinations (sometimes whether or not these rearrangements are desirable). A few considerations of scale are important in understanding this process. Atoms comprise a positive nucleus and a surrounding cloud of negative electrons. These charges rearrange when another atom approaches, with unlike charges shifting to give rise to the van der Waals force of attraction between neutral atoms. This force makes gravity (and most accelerations) ignorable when contact between solid objects in the micrometer size range and smaller is involved, since surface-to-volume ratios are inversely proportional to object size.

The electric field in the scanning tunneling microscope allows plucking as well, in which adsorbed or substrate atoms are removed and transferred to the electrode tip with a suitable voltage pulse. Because the electric field from the tip falls off less rapidly with separation than do van der Waals forces, the most weakly attached nearby atom rather than the nearest may end up being removed. One solution to this problem is a hybrid approach. By invoking the tip electric field for bond breaking only when the tip is sufficiently close to the target atom that the van der Waals forces contribute as well, atoms on silicon could be singly removed and redeposited at will.

A third kind of selective bond breaking was also demonstrated. It involved the selective breaking of silicon-hydrogen bonds using electron energies (that is, pulse voltages) below those necessary to break bonds directly. Since the desorption probability was observed to vary exponentially with the tip-specimen current, it is believed that vibrational heating from inelastic electron tunneling mediated the chemical transition in this work. This work involves bond alteration at the level of signal atoms, the ultimate frontier for lithographic miniaturization.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

scanning tunneling microscope

[′skan·iŋ ¦tən·əl·iŋ ′mī·krə‚skōp]
An instrument for producing surface images with atomic-scale lateral resolution, in which a fine probe tip is raster-scanned over the surface at a distance of 0.5-1 nanometer, and the resulting tunneling current, or the position of the tip required to maintain a constant tunneling current, is monitored. Also known as tunneling microscope.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Lu, "Atomic resolution scanning tunneling microscope imaging up to 27 T in a watercooled magnet," Nano Research, vol.
The team used a highly stable scanning tunneling microscope (STM) to create a transistor consisting of a single organic molecule and positively charged metal atoms, positioning them with the STM tip on the surface of an indium arsenide (InAs) crystal.
When a molecule was centered on a tiny bump, a nudge with the scanning tunneling microscope sent the legs of the molecule gently rotating, while the center stayed stationary.
One variety of SPM, the scanning tunneling microscope, uses a stream of electrons to image the surface without quite touching it.
Among the devices there were presented in the field of nanotechnology in the Second Exhibition of Laboratory Devices and Materials Made in Iran, mention can be made of products such as scanning tunneling microscope, atomic force microscope, vibrating sample magnetometer, electrospinning, capillary electrophoresis, various coating and deposition systems, gas and two-dimensional chromatography equipment, porosimetry and specific area measurement systems, and metallic nano-colloid and nanopowder production equipment.
"We were able to achieve this by studying specially made nanoribbons with a scanning tunneling microscope."
Cyrus Hirjibehedin of IBM's Almaden Research Center, in San Jose, Calif., and his colleagues used a scanning tunneling microscope to place iron or manganese atoms on a copper-nitrogen surface and to sense the atoms' spins--the atomic version of their magnetic axes.
Light emission from a scanning tunneling microscope was used to investigate the electromagnetic coupling between a metal tip and a metal surface.
The Piezolever serves as an atomic force microscope (AFM) and the metal tip serves as a scanning tunneling microscope (STM).
Among the devices in the laboratories, mention can be made of scanning tunneling microscope (STM), electrospinning devices to produce nanofibers, electrical explosion, and on-board sputtering.
The scanning tunneling microscope used in the present study features a delicate electrode tip held very close to the DNA sample.
On copper (black), each anthraquinone molecule appears in this scanning tunneling microscope image as a mound that's orange or yellow on top, green in the middle, and blue at the base.

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