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From physnews@aip.org Wed Oct 15 14:00:06 1997 Date: Wed, 15 Oct 97 10:28:48 EDT From: physnews@aip.org (AIP listserver) Message-Id: <9710151428.AA08697@aip.org> To: physnews-mailing@aip.org Subject: update.341

PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 341 October 15, 1997 by Phillip F. Schewe and Ben Stein

THE 1997 NOBEL PRIZE FOR PHYSICS has been won by

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THE FIRST SOLID MATERIAL THAT CAN REVERSIBLY SWITCH BETWEEN METAL AND INSULATOR at room temperature and pressure, and without changing its chemical makeup, has been created by researchers at UCLA (James Heath, heath@chem.ucla.edu). The researchers prepare a Langmuir film, an ultrathin layer of material on a water surface. The film consists of a 2-D hexagonal pattern of silver nanocrystals (only nm size) with each nanocrystal's surface capped by compressible organic molecules. Applying pressure to the film can decrease the distance between adjacent nanocrystals from 12 to 5 angstroms. When compressed, the film becomes shiny and its optical properties match those of a thin metal film. Prior to compression, the film has the optical properties of an insulator: in this state, the nanocrystalsbehave as semi-isolated particles and they do not share electrons. As the separation between nanocrystals decreases, the researchers observe a transition from "classical coupling" (adjacent nanocrystals induce the movement of charge in each other and thereby transfer energy) to "quantum coupling" (nanocrystals begin to share electrons simultaneously and electrons delocalize, or cease to occupy a specific position in the material). (C. P. Collier et al, Science, 26 September 1997)