Carbon nanotubes (CNTs)—graphene sheets wrapped into hollow cylinders a nanometer or two in diameter—have inspired a vast array of proposed applications based on their many extraordinary characteristics. They’re mechanically strong, flexible, and lightweight. And their structure-dependent electronic and optical properties make them ideal components for FETs, photonic systems, and more. (See the article by Phaedon Avouris, Physics Today, January 2009, page 34.)
A CNT’s atomic structure is defined by a pair of indices (n,m), which together determine its diameter and the orientation of the graphene lattice with respect to the tube’s axis. (See the article by Cees Dekker, Physics Today, May 1999, page 22.) When n and m are equal, the electronic bandgap is zero, and the CNTs are metallic. When n − m is a multiple of three, the bandgap is small, and the CNTs are deemed semimetallic. Most other index...
