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Buckyballs shine as optical materials.

Nonlinear optical films can streamline optical communications and could eventually make the dream of optical computing come true. Buckyballs--those 60-carbon molecules shaped like soccerballs (see story, p.120) -- now show promise as one such material, two research groups report.

Nonlinear optical materials vary in their light-processing potential. Some show second-order properties: They double the frequency of the light passing through them and cease to transmit light when subjected to an electric field. Others show third-order properties: They triple the frequency of the light passing through them and switch on or off depending on the light's intensity. Buckyball compounds seem to do both fairly well, says Ying Wang, a physical chemist at the Du Pont Experimental Station in Wilmington, Del.

Using solutions of molecules, Wang studied the light-altering properties of buckyballs alone and of buckyballs linked with another material in a so-called charge-transfer complex. Buckyballs alone exhibit third-order properties, but the buckyball-containing complex lacks the symmetry of the solo molecules and thus adds second-order properties to the compound, reports Wang.

Zakya H. Kafafi, a chemist at the Naval Research Laboratory in Washington, D.C., decided to look into the buckyball's light-altering properties because the fluctuating double and single bonds between its atoms resemble those of other nonlinear optical organic materials. Unlike Wang's group, Kafafi measured optical properties in a buckyball thin film. She also tried depositing these brown films on materials used in optics, including glass, quartz and gold. "They adhere to all these surfaces very nicely," Kafafi says.

Buckybal films remain more stable chemically than most materials with comparable nonlinear optical potential, Wang says. And unlike other organic materials with this potential, buckyballs lack carbon-hydrogen and hydrogen-oxygen bonds, which can interfere with some nonlinear optical properties. Moreover, research on buckyball superconductors indicates that scientists can make these thin films easily and can chemically modify them to suit particular purposes. "It's a good potential nonlinear optical material," Kafafi concludes.

Both researchers presented their findings in Philadelphia this month at the University of Pennsylvania Workshop on Fullerites and their Solid-State Derivatives.
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Publication:Science News
Date:Aug 24, 1991
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