True properties of carbon nanotube...( EVANSTON Ill. --- For more than 15 y...)

EVANSTON, Ill. --- For more than 15 years, carbon nanotubes (CNTs) have been the flagship material of nanotechnology. Researchers have conceived applications for nanotubes ranging from microelectronic devices to cancer therapy. Their atomic structure should, in theory, give them mechanical and electrical properties far superior to most common materials.

Unfortunately, theory and experiments have failed to converge on the true mechanical properties of CNTs. Researchers at Northwestern University recently made the first experimental measurements of the mechanical properties of carbon nanotubes that directly correspond to the theoretical predictions.

Carbon nanotubes are cylindrical structures usually less than 30 nanometers in diameter and several microns long. Their small size makes them very strong but at the same time quite difficult to test individually; as a result, experiments typically deviate widely from predictions based on quantum mechanics.

"Imaging and measurement resolutions as well as atomic structural ambiguities (defects) obscured the results of most experiments and provided unreliable mechanical predictions," said Horacio Espinosa, a professor of mechanical engineering at Northwestern's McCormick School of Engineering and Applied Science.

Espinosa and his group at Northwestern have resolved these issues using a nanoscale material testing system based on microelectromechanical system (MEMS) technology. This system allows electronic measurements of load and displacement during a test, which is performed inside a transmission electron microscope to provide real-time atomic imaging.

"This method removes all ambiguity from testing results," Espinosa said. "We can be certain of all the quantities we have measured, and the results match quantum mechanics predictions very well."

Espinosa collaborated with George Schatz, Morrison Professor of Chemistry in Northwestern's Weinberg College of Arts and
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