  The cutting of single-walled carbon nanotubes by an 80 keV electron beam
catalyzed by nickel clusters is imaged in situ using aberration-corrected
high-resolution transmission electron microscopy. Extensive molecular dynamics
simulations within the CompuTEM approach provide insight into the mechanism of
this process and demonstrate that the combination of irradiation and nickel
catalyst is crucial for the cutting process to take place. The atomistic
mechanism of cutting is revealed by detailed analysis of irradiation-induced
reactions of bonds reorganization and atom ejection in the vicinity of the
nickel cluster, showing a highly complex interplay of different chemical
transformations catalysed by the metal cluster. One of the most prevalent
pathways includes three consecutive stages: formation of polyyne carbon chains
from carbon nanotube, dissociation of the carbon chains into single and pairs
of adatoms adsorbed on the nickel cluster, and ejection of these adatoms
leading to the cutting of nanotube. Significant variations in the atom ejection
rate are discovered depending on the process stage and nanotube diameter. The
revealed mechanism and kinetic characteristics of cutting process provide
fundamental knowledge for the development of new methodologies for control and
manipulation of carbon structures at the nanoscale.
