Observation of Nanometer-Scale Rolling Motion Mediated by Commensurate Contact

We report, through experimental observations and computer simulations, that atomic lattice interlocking can determine whether an object rolls or slides on a surface. We have quantitatively manipulated carbon nanotubes (CNTs) on a variety of substrates with an atomic force microscope (AFM) and observe rolling to occur only on graphite. We measure the forces when the CNT is in-registry with the graphite lattice, and observe rolling only in this lock-in state. Atomistic computer simulations identify the energy barriers for sliding and rolling, elucidate atomic-scale features of slip-roll motion, and explain the details of the lateral force data in terms of the intrinsic faceting of multiwall CNTs.