Study of CNT growth termination mechanism: Effect of catalyst diffusion

Carbon nanotube (CNT) growth termination mechanism has been studied using Molecular Dynamic (MD) simulation. Due to catalyst diffusion and interaction between the catalyst and the CNT growth substrates, the catalytic activity needed for CNT nucleation is depleted. Diffusion coefficient of the Fe catalyst on different substrates has been evaluated using averaged mean square displacement (MSD) of the Fe atoms in the simulation. At the CNT growth temperature, Fe on Cu substrate shows the highest diffusion coefficient. The calculated low diffusion coefficient of Fe atoms in Al₂O₃ substrate confirms the use of Al₂O₃ as the choice material for the diffusion buffer layer. This is consistent with observations in CNT growth experiments using thermal chemical vapor deposition (CVD). The MD simulation provides a clear demonstration of Al₂O₃ as an effective diffusion buffer material.