Nanotubes continue to promise endless applications

17 Jun 2002

Nanotubes, stiffer than steel, only a nanometer wide but many microns long, are essentially rolled-up sheets of carbon hexagons. Scientists are finding myriadapplications for these structures, which one researchers calls "more precious than platinum."

Richard Smalley of Rice University, winner of the 1996 Nobel Prize in chemistry for his discovery of buckyballs in 1985, reports that his lab currently producesnanotubes at a rate of grams/day but predicts within 5 to 10 years this could be increased to a commercial grade of tons per day. In recent research Smalleydemonstrated nanotubes that swallow their own tails, forming closed toruses. In another configuration, Smalley showed bundles of nanotubes in which one tubestuck out further than its neighbors. Nested stages of such bundles, he said, could be used to fashion pointers-- macroscopic at one end but tapering down to a singlecarbon cell at the other end-- with which one could (like an artist dipping a paintbrush into a palette of colors) "write" patterns of molecules on a substrate.

Electrically, the versatile nanotubes can be insulators, semiconductors, or conductors and are expected to exhibit magnetoresistance qualities. The pointy nanotubespromise use as field emitters in flat panel displays. Attaching a semiconducting nanotube to a metallic nanotube one gets a nano-diode. If the joint is angled, thecomposite tube can make the structure into a possible nanoswitch or strain gauge.

Meanwhile, Cees Dekker of Delft University has studied the electron transport properties of single nanotubes by draping them across a pair of electrodes. Thecurrent-versus- voltage plot is a series of steps, indicative of a "quantum wire." At Lawrence Berkeley Laboratory, Steven Louie has worked with nanotubes made ofboron and nitrogen, or of carbon mixed with B and N. In one configuration, a Louie reports the ribbon of conducting carbon hexagons forms a corkscrew pattern upthe length of the tube. The current flow through such a tube is helical creating, in effect, the world's smallest solenoid magnet.