Ability to Control Configuration and Length of Nanotubes Demonstrated
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RESEARCH/RESEARCHERS Ability to Control Configuration and Length of Nanotubes Demonstrated The ability to control the structure and arrangement of carbon nanotubes (CNTs) is a prerequisite to realizing many nanoscale applications. Researchers from Rensselaer Polytechnic Institute (RPI) in Troy, N.Y., and from Tsinghua University in Beijing have discovered methods for arranging CNTs into specific configurations that exhibit distinct electrical and mechanical properties. These techniques have recently been reported in Science and Nature. As reported in the May 3 issue of Science, teams led by P.M. Ajayan at RPI and H.W. Zhu at Beijing University have developed an optimized catalytic chemical vapor deposition (CVD) technique that can be used to synthesize long, continuous strands of single-walled nanotubes (SWNTs). The researchers introduced an n-hexane solution composed of ferrocene and thiophene into a vertical reactor heated to the pyrolysis temperature and flowed hydrogen as the carrier gas. The usual CVD processes that are used to create SWNTs typically result in nanotube bundles that are tens of micrometers in
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length. In the researchers’ technique, the reaction temperature and hydrogen flow rates were optimized to create a continuous process that yielded macroscopic strands of SWNTs up to several centimeters in length. The use of n-hexane, as opposed to other hydrocarbons, and a hydrogen carrier gas was crucial to achiev-
ing high SWNT yields and large selfassembled strands. Resistivity measurements on as-grown SWNT strands with lengths ranging from 10 cm to 20 cm and diameters ranging from 50 µm to 0.5 mm were low enough to indicate that macroscopic lengths of conducting paths or nanotubes existed in the strands. Estimates of
SWNTs Ignite Ignite on SWNTs on Exposure Exposureto toaaCamera CameraFlash Flash
In an RPI, IPCYT in Mexico, the University of Sussex England, In an alliance alliancebetween between RPI, IPCYT in Mexico, the University of in Sussex in and Université Louis Pasteur in France, Ajayan, M. Terrones, accidenEngland, and Université Louis Pasteur in France, Ajayan,and M. co-workers Terrones, and cotally discovered thatdiscovered SWNTs ignite exposed to a photographic flash from a workers accidentally that when SWNTs ignite when exposed to a photographAs reported in As the reported April 26 issue Science, ignition effectan occurs in SWNTs iccamera. flash from a camera. in theofApril 26 an issue of Science, ignition effect prepared by carbon arc, laserby ablation, CVD upon exposure to a camera flash within occurs in SWNTs prepared carbonor arc, laser ablation, or CVD upon exposure to of several the CNT. The researchers foundWhen that the average lightinpower aseveral cameracentimeters flash within centimeters of the CNT. local increases tem2 for carbon, a sampleignition density and of 0.2 g/cm3. necessarycaused for SWNT was ~100 mW/cm perature by aignition flash initiate oxidation of the burning When local increases in temperatu
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