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update.341 (fwd) [edited]




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> From [email protected] Wed Oct 15 14:00:06 1997
> Date: Wed, 15 Oct 97 10:28:48 EDT
> From: [email protected] (AIP listserver)
> Message-Id: <[email protected]>
> To: [email protected]
> 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

[text deleted]

> 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,
> [email protected]).  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)
>