Controlling the Structure and Properties of Carbon Nanotubes

Carbon nanotubes are a hollow, cylindrical form of elemental carbon that was discovered by Sumio Iijima in 1991 [1]. These carbon tubes are typically one to several nanometers in diameter and tens of microns in length, although nanotubes several centimeters have been synthesized. Nanotubes are considered both the stiffest and strongest materials known to man, and have Young's moduli and tensile strengths that are orders of magnitude greater than high-performance metals. Electrically, they are capable of ballistic (scattering-free) transport of electrons at very high current densities, as well as highly-efficient electron emission. Carbon nanotubes also are stable at high temperatures and have very high thermal conductivities. These properties make carbon nanotubes well-suited for a wide range of applications. Some of these applications now are beginning to reach commercial maturity, with carbon nanotubes being used as probe tips for atomic force microscopes and as field emitters for next-generation displays. Increased control over the structure of carbon nanotubes will be required, however, before advanced nanotube-based electronic devices can take full advantage of nanotubes' remarkable properties. This structural control, which may be achieved by developing novel synthesis or extraction processes capable of producing or isolating nanotubes with uniform electrical properties, could enable the development of sophisticated nanotube-enabled computers, memories, or sensing devices. This report reviews the progress that has been made toward developing these processes, and provides a summary of the methods currently available for controlling or influencing the structure and properties of carbon nanotubes.