Carbon Nanotubes Can "Remember" Their Initial Structure, Isotope Labeling Reveals Dynamic Growth Process

A study released on September 1 shows that carbon nanotubes can maintain their initial atomic structure in dynamically changing growth environments. The research team used digital isotope labeling technology to encode the elongation process of individual carbon nanotubes as sequences of different carbon isotope compositions, and read their growth history through Raman spectroscopy, thereby tracking the structural stability of nanotubes under conditions of temperature variation and catalyst evolution.

The properties of carbon nanotubes are highly dependent on their atomic arrangement. The same material may exhibit metallic or semiconducting characteristics due to structural differences, so structural uniformity has always been a key issue for the large-scale application of carbon nanotubes. In industrial production routes such as floating catalyst chemical vapor deposition, catalyst particles experience constantly changing temperatures and gas compositions within the reactor and may undergo irreversible enlargement. Previously, direct evidence was lacking on whether individual carbon nanotubes could maintain their initial structure under such complex conditions.

In this study, the team employed ethanol pulses containing different proportions of carbon isotopes to perform "digital labeling" on growing carbon nanotubes, reconstructing the elongation process of individual nanotubes with a 30-second temporal resolution. The results showed that when the furnace temperature was raised from 800°C to 873°C and then lowered, the growth rate of nanotubes at the same temperature reached approximately twice that before the temperature increase. This hysteresis phenomenon indicates that the catalyst underwent irreversible coarsening during the high-temperature process.

However, the changes in growth rate did not lead to structural alterations in most nanotubes. The study showed that even when carbon nanotubes exceeded 100,000 times their diameter in length, they still maintained atomically consistent lattice structures. Among the 158 carbon nanotubes analyzed, 139 maintained their chirality unchanged within the measured length range, accounting for approximately 88%. The study also combined kinetic Monte Carlo simulations and molecular dynamics simulations, further supporting that catalyst coarsening alters growth rates but does not necessarily change the diameter and chirality of already-formed nanotubes.

The researchers believe this indicates that the structure of carbon nanotubes is primarily determined during the nucleation stage and exhibits strong "structural memory" during subsequent elongation stages; in contrast, growth rates remain sensitive to environmental factors such as temperature and catalyst state. This separation between structure determination and growth kinetics provides a new design approach for carbon nanotube synthesis: structural control can be optimized during the nucleation stage, while yield can be enhanced during the elongation stage, thereby alleviating the long-standing trade-off between quality and quantity.