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Tiny semiconductor can't take the heat.

Scientist used to think every material exhibited a characteristic melting point. During the past 20 years, however, researchers have realized that when they make extremely tiny particles of metals, inert gases or molecular crystals, the melting point drops, sometimes by a lot. Now Avery N. Goldstein and his colleagues at the University of Californiaa, Berkeley, have shown that semiconductors also behave this way.

The researchers observed spherical nanocrystals of cadmium sulfide using transmission electron microscopy. When they heated the crystals, they saw the smallest crystals melted at a temperature 1,000 kelvins lower than bulk cadmium sulfide, Goldstein and his colleagues report in the June 5 SCIENCE.

"From a practical viewpoint, it's a big drop," says A. Paul Alivisatos, the chemist who headed the Berkeley group. Electronic components are rapidly shrinking to submicrometer dimensions, small enough that these effects may inhibit a component's ability to function at high temperatures.

With just a few hundred or a few thousand atoms per particle, the lower number of atoms overall translate into lower cohesive energy for the particles, says Alivisatos. Thus the atoms can escape the solid phase much more readily.
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Title Annotation:particles of metals, inert gases, molecular crystals
Publication:Science News
Article Type:Brief Article
Date:Jun 20, 1992
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