Growth Mechanism of Double-Walled Carbon Nanotubes: Insights from Density Functional Theory Computations

The growth mechanism of double- or multi-walled carbon nanotubes (DWCNTs or MWCNTs) via floating catalyst chemical vapor deposition (FCCVD) is still an uncharted territory, despite its significance in achieving controlled synthesis of carbon nanotubes (CNTs) with desired material properties. To address this knowledge gap, we employed Density Functional Theory (DFT) computations to investigate the stability and growth of DWCNT caps and shorter tubular segments on the surface of icosahedral Fe147 and Fe309 nanoparticles. Both zigzag and armchair CNTs with different diameters were considered as inner and outer tubes in our model systems. The tube growth was found to be mainly dependent on the diameter, while chirality plays a minor role. Furthermore, the results reveal that while the formation and growth of the outer tube are more favorable, its presence promotes the growth of the inner tube. Our findings suggest that the growth of inner and outer tubes in the FCCVD process occurs simultaneously rather than following a layer-by-layer mechanism. Overall, this study provides valuable insights into how nanoparticle and tube diameters influence the growth of DWCNTs.