Nanometer Sized Particles Change Structure When Wet - New Technology

University of California, Berkeley, scientists have found an unusual effect that could have both good and bad implications for semiconductor devices once they've been shrunk to the nanometer scale.

The discovery also could provide a way to tell whether pieces of rock from outer space came from planets with water.

In a paper appearing in the Aug. 28 issue of Nature, a UC Berkeley team comprised of physicists, chemists and mineralogists reports on the unusual behavior of a semiconducting material, zinc sulphide (ZnS), when reduced to pieces only 3 nanometers across - clumps containing only 700 or so atoms.

They found that when the surface of a ZnS nanoparticle gets wet, its entire crystal structure rearranges to become more ordered, closer to the structure of a bulk piece of solid ZnS.

"People had noticed that nanoparticles often had unexpected crystal structures and guessed it might be due to surface effects," said post-doctoral physicist Benjamin Gilbert of UC Berkeley's Department of Earth & Planetary Science. "This is a clear-cut demonstration that surface effects are important in nanoparticles."

Gilbert and co-author Hengzhong Zhang, a research scientist and physical chemist, suggest that many types of nanoparticles may be as sensitive to water as ZnS.

"We think that, for some systems of small nanoparticles maybe 2 to 3 nanometers across, this kind of structural transition may be common," Zhang said.

"There's a good and bad side to this," Gilbert added. "If we can control the structure of a nanoparticle through its surface, we can expect to produce a range of structures depending on what molecule is bound to the surface. But this also produces unexpected effects researchers may not want."

In addition, Zhang said these effects could have implications for our understanding of extraterrestrial materials and identification of extraterrestrial rocks, especially when the interpretation is being done by a robotic probe. A nanoparticle that formed in a place with water, such as Earth, would have a more ordered surface than a nanoparticle formed in space, where water is not present.

Understanding how the characteristics of specific nanomaterials vary with environment could also lead to their use as sensors, for example, for water.

Posted 27th August 2003

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