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Atomic bonds: seeing the links.

Atomic bonds: Seeing the links

The invention of the scanning tunneling microscope (SN:4/2/83, p.213) and later refinements have allowed increasingly sharper views of atoms perched on solid surfaces. The latest advance brings pictures not only of silicon atoms neatly arrayed on a silicon surface but also of the bonds holding the atoms in place.

A scanning tunneling microscope uses the tiny electric current that flows between a probe tip and a sample, only a few atomic diameters apart, to trace out a contour map of the sample's surface atoms. As the probe is moved back and forth across the sample, its vertical height is continually adjusted to keep the current constant. Normally, the voltage applied between the sample and probe also stays the same.

In this case, scientists at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., periodically hold the probe still while varying the voltage. This provides a map of how the current varies at selected points over a surface. The information is then used to show where electrons bonding surface atoms are likely to be.

The picture at left shows a theoretical model, confirmed by earlier microscopic views, of a silicon atomic structure, magnified about 30 million times. The diamondshaped outline reveals the repeating unit that makes up the complete surface. The picture at right shows wispy bonds that reach up from a sample's second atomic layer and connect with surface atoms, seen as bright spots.
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Publication:Science News
Date:Sep 6, 1986
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