Molecular dynamics of carbon nanotubule proximal probe tip-surface contacts

The mechanisms by which carbon nanotubule (CNT) proximal probe tips deform during the indentation of surfaces are explored using classical molecular-dynamics simulations. The forces acting on the atoms in the simulations are calculated using the Brenner empirical bond-order potential for hydrocarbons. The results show that open and capped single-walled CNT tips indented against hydrogen-terminated diamond and graphene surfaces buckle and slip to relieve the applied stress. The study also examines the indentation of capped multiwalled tubules against these surfaces to investigate the effect of multiple shells on the deformation process. It is found that while shell-shell interactions have little effect on the deformation mechanisms, the multiwalled tubule is significantly stiffer than comparably sized single-walled tubules. No bond formation between the shells is predicted as a result of deformation. Finally, a small CNT rope is indented against diamond and graphene to assess the effect of intertubule interactions on deformation. The simulations reveal how the deformation of the rope leads to the distortion of its end and allow for the determination of the effect of shear stress within the bundle on the buckling force of the rope.