By Peter Weiss
From Minneapolis, at a meeting of the American Physical Society
Rolling, rolling, rolling. Keep those nanotubes rolling.
Carbon nanotubes are slender, hollow, cylindrical molecules of pure carbon. Extraordinarily strong and flexible, with intriguing electronic properties, the microscopic tubes offer scientists pure fascination (SN: 8/21/99, p. 127).
Now, Michael R. Falvo and Richard Superfine of the University of North Carolina at Chapel Hill and their colleagues may have discovered why the tubes sometimes roll and at other times slide when pushed across a graphite surface by the tip of an atomic-force microscope.
From experiments and computer simulations, the researchers find evidence that tubes roll only when the honeycomb lattice of the carbon atoms meshes with graphite’s identical carbon lattice.
“That’s very exciting,” Falvo says, partly because it suggests that nanotubes are fulfilling a long-held dream of nanotechnology pioneers: gears with atoms as teeth.
“Crazy ideas people had about nanotechnology maybe are not so crazy after all,” Falvo says. Using a virtual-reality computer setup to control the microscope tip (SN: 1/13/96, p. 31) that pushes nanotubes, Falvo and his coworkers found that, most often, tubes pivot. This sliding motion occurs unless tubes lie along one of three orientations that are 60º apart from each other.
Both force data and computer models that Falvo presented suggest a gearlike meshing between the graphite and the tubes in each of the three special orientations. Dislodging an oriented tube yields a force pattern different from that seen when a tube pivots. The findings indicate that rolling, rather than sliding, is then taking place, Falvo says.
