Nanobots walk 'n' roll.

One wobbles forward as a toddler does. The other's movement is more like a car's. Such motions might not seem like much, but getting tiny molecular constructions to execute them is quite a feat, say scientists from two independent teams that have demonstrated the molecular motions.

To create their walking nanobot, Ludwig Barrels of the University of California, River-side and his colleagues there and at Kansas State University in Manhattan retrofitted a benzene-based molecule so that it has what amounts to two feet, each a sulfur atom. Thermal energy causes the feet to repeatedly attach to and detach from a copper surface, resulting in a straight walking motion, the researchers report in the Oct. 14 Physical Review Letters. That's a big step toward controlling random molecular wandering, or diffusion, on surfaces, Bartels says. He adds that such precisely controlled movement could improve catalysis and data storage.

To build their carlike nanobots, James M. Tour of Rice University in Houston and his colleagues attached sets of four spherical, all-carbon molecules called fullerenes to stiff chassis made of linked benzene compounds.

In an upcoming Nano Letters, the Rice team demonstrates that the vehicles, powered by thermal energy, roll across a gold surface rather than slide haphazardly. The cars sometimes pivot a bit, but Tour says that shouldn't be a problem because electric fields can be used to direct vehicle motions. Such nanoscale vehicles might shuttle around components during construction of nanoscale electronic devices and other structures.-P.W.