Molecular dynamics simulations of carbon nanotube rolling and sliding on graphite

Molecular dynamics simulations were carried out to investigate the origin o f friction for carbon nanotubes on graphite substrates. In an initial simul ation, a (10,10) nanotube was placed in an 'in-registry' starting position where the hexagonal lattice of the substrate matched that of the nanotube. In a second simulation, the substrate was oriented 90 degrees to the nanotu be. A uniform force was applied to the nanotubes for 500 fs to set them int o motion. The simulation was then run until the nanotubes stopped moving re lative to the substrate. Only sliding was observed in the out-of-registry s imulation, while periodic sliding and rolling was observed in the in-regist ry simulation. The latter is a result of the relatively larger surface corr ugation for the inregistry case and occurs to avoid direct atomic collision s between nanotube and substrate atoms as the nanotube is moved along the s ubstrate. Analysis of the kinetic energy suggests that the transition betwe en sliding and rolling contributes to enhanced energy dissipation and highe r net friction. These results are consistent with preliminary experimental observations by Superfine and coworkers.