Carbon nanotubes are candidate lubricant materials for microelectomechanical systems (MEMS) and  nanoelectromechanical systems (NEMS). Here we investigate the tribological responses of bundles of single-walled nanotubes (SWNTs) and filled SWNTs to compressive and shear forces between two hydrogen-terminated sliding diamond surfaces by using classical molecular dynamics simulations with the second-generation REBO potential.

      The carbon nanotube bundle consists of six (10,10) single walled nanotubes that are about 55 Å long and have caps at both ends. The nanotube bundle is placed between the diamond (111) surfaces. Each diamond substrate has 12 carbon layers and is terminated at both ends with hydrogen atoms. The snapshots of the initials structures are shown in Fig. 1. The outermost hydrogen atoms and two carbon layers are held fixed and the next four layers of carbon atoms have Langevin frictional forces applied to them. Any other carbon atoms in the diamond substrates and the nanotubes and the innermost hydrogen atoms are the active atoms, which follow Newtonian motion with no additional constraints. Each nanotubes in Fig. 1(b) is filled with four C₆₀ fullerenes. The systems are allowed to equilibrate fully at 300K before external forces are applied. The nanotube bundles are subjected to compressive forces followed by shear forces that are carried out by moving the upper diamond substrate by 0.05 Å every 625 steps or 40 m/s. The forces are measured at the topmost atoms of upper diamond substrate from last 100 of iterations. The change in the compressive forces of these systems as a function of uppermost diamond substrate displacement is shown in Fig. 2.