Solid-solid-vapor catalytic etching of carbon nanotubes investigated by in situ transmission electron microscopy

Understanding the catalyst-assisted etching mechanisms of carbon nanotubes (CNTs) is essential for structure tailoring and stability enhancement. This process occurs in an oxidizing atmosphere with catalyst nanoparticles (NPs) in direct contact with the nanotubes, however, its atomic-scale mechanisms have long been overlooked due to the challenge of capturing real-time dynamics at the CNT-NP interface. Using atmospheric-pressure environmental transmission electron microscopy, we grow CNTs directly from cobalt NPs to construct a well-defined CNT-NP interface, enabling us to investigate the etching dynamics in real time. We demonstrate that catalytic oxidation at this interface efficiently etches CNTs under mild oxidative conditions, with etching rates approximately six times higher than those of direct oxidation and an activation energy of 1.9 eV. Orthorhombic Co₃C is precisely identified as the active phase of the catalysts during oxidative etching, and it remains stable until the CNT is completely consumed. Contrary to the conventional solid-vapor gasification mechanism, we reveal a solid-solid-vapor (SSV) catalytic etching mechanism for CNT oxidation, which inherently involves metal-mediated carbon gasification. Moreover, even when starting as an oxide, the NP is converted into a carbide via the SSV mechanism through chemical reaction with the attached CNT.