Breaking the Axis-Symmetry of a Single-Wall Carbon Nanotube During Its Growth.

The asymmetrical growth of a single-wall carbon nanotube (SWCNT) by introducing a change of a local atomic structure, is usually inevitable and supposed to have a profound effect on the chirality control and property tailor. However, the breaking of the symmetry during SWCNT growth remains unexplored and its origins at the atomic-scale are elusive. Here, environmental transmission electron microscopy is used to capture the process of breaking the symmetry of a growing SWCNT from a sub-2-nm platinum catalyst nanoparticle in real-time, demonstrating that topological defects formed on the side of a SWCNT can serve as a buffer for stress release and inherently break its axis-symmetrical growth. Atomic-level details reveal the importance of the tube-catalyst interface and how the atom rearrangement of the solid-state platinum catalyst around the interface influences the final tubular structure. The active sites responsible for trapping carbon dimers and providing enough driving force for carbon incorporation and asymmetric growth are shown to be low-coordination step edges, as confirmed by theoretical simulations.