Image: L. D. MARKS/Northwestern University
Most nanotubesminuscule straws marveled for their strength and unique electronic propertiesare made from pure carbon. But a better alternative in some cases might be similarly tiny tubes made from boron nitride (BN). Indeed, BN nanotubes promise to be less fragile, chemically speaking: they have a higher tolerance to heat and are less likely to oxidize. "Carbon's great stuff," says Laurence Marks of Northwestern University, "but boron nitride can be just as great, if not greater."
Unfortunately, scientists studying BN nanotubes have been unable to produce images of their creations in the absence of airwhich some fear contaminates the results. Now Marks and his colleagues have discovered a way around that difficulty, which they describe in this week's issue of Physical Review Letters.
In an ultrahigh vacuum, they sprayed boron and energetic nitrogen atoms onto a heated tungsten surface so that the nanotubes grew as a kind of hair at a rate of about one angstrom per second. They compared electron micrographs of the result with computer models (see image) and discovered that the closed rings on the ends of the tubes contained four and eight atoms, instead of the five- and seven-atom rings on their carbon cousins. As for applications, Marks suggests that BN nanotube hair might be used to reduce friction on bearings in heavy machinery.