Electron beam-induced changes in tips of multi-walled carbon nanotubes with/without Au nanoparticles

Tips of multi-walled carbon nanotube of dissimilar shapes with/without gold nanoparticles are irradiated under electron beam. The tips become meta-stable and cause reduction in lengths of tubes under a high intense uniform electron beam by their smaller radius of curvature when the diffusion and evaporation of carbon atoms are activated. Meanwhile, normal-tube-tips and volcano-tube-tips with/without gold nanoparticles present dissimilar changes in their diameters. The gold nanoparticles with size ≥ 3 nm not only slow down length reduction process in the normal-tube-tips and increase tips diameters but also increase their size on the normal-tube-tip by the interaction and growth, while gold nanoparticles with size ≤ 1.5 nm retard the length reduction process in volcano-tube-tips without any change in the tips diameters. Furthermore, they also activate formation of carbon shells over their surface and keep their positions fixed on the volcano-tube-tip. This abnormal interaction of gold nanoparticles with the unstable tips is elucidated in terms of irradiation-induced activation of the graphitic layers, diffusion of Au atoms and bonding between adjacent large (≥ 3 nm) Au NPs, and catalytic effects of small (≤ 1.5 nm) Au NPs. The method can be employed to modify nanotubes with almost atomic precision and to create a predefined pattern of metal nanoparticles on tube tips and surface.