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The Next Big Thing:
Measuring the Tiniest of Structures

Nanoscience provides a promising collection of materials for a new generation of devices and structures. But before these new materials go to work, their properties must be thoroughly understood and documented.

Carbon nanotubes offer intriguing potential applications, but to use them scientists must gain a thorough understanding of their materials properties. Georgia Tech researchers use mechanical resonance induced by an oscillating electrical voltage to measure the bending strength of the tubes.

Georgia Tech researchers Walter de Heer and Zhong L. Wang use a straightforward technique – mechanical resonance induced by an oscillating electrical voltage – to measure the bending strength of carbon nanotubes produced by two different processes.

The work, which also correlates strength measurements to observable defects, will help engineers select the right type of nanotube for new applications as diverse as ultra-light composites and low-power field emission displays.

"We are able to make a quantitative comparison, with a real number to describe how the bending modulus differs," explains Wang, director of Georgia Tech's Center for Nanoscience and Nanotechnology, and a professor in the School of Materials Science and Engineering. "This work gives theoretical scientists data to model individual nanotubes."

Wang and de Heer – a professor in the School of Physics – compare nanotubes produced by high-temperature carbon arc discharge to structures grown in a catalyst-assisted pyrolysis process. In the latter, they found significant strength differences caused by point and volume defects.

Wang believes catalytically grown nanotubes offer advantages for lightweight composites, where defects could help interlock tubes to keep them from pulling out of the matrix. However, those same defects could cause problems in electronic applications, where nanotubes produced by carbon arcs may be superior.

Measurement begins by gluing a single nanotube to a tiny gold ball in a specially prepared transmission electron microscope sample holder. The tube is aligned near another gold ball, and an oscillating electrical voltage applied. Adjusting the frequency induces a measurable mechanical resonance in the tube.

By knowing the outer diameter, inner diameter and density of the nanotube, researchers can determine the bending modulus from the frequency at which it resonates. Observation in the transmission electron microscope correlates defects with strength.

Wang and de Heer also measured the conductance of a single carbon nanotube at room temperature. The current density that a single nanotube can carry is higher than any other material at room temperature, suggesting the possibility of using carbon nanotubes as interconnections in nanoelectronics. The work was reported in the journal Science.

For more information, contact Zhong Wang, School of Materials, Science and Engineering, Georgia Tech, Atlanta, GA 30332-0245. (Telephone: 404-894-8008) (E-mail: zhong.wang@mse.gatech.edu);   or Walter de Heer, School of Physics, Georgia Tech, Atlanta, GA 30332-0430. (Telephone: 404-894-7879) (E-mail: deheer@electra.physics.gatech.edu)