The Phase Transition Mechanism of Solid Nanoparticles During Catalytic Growth of Single-Walled Carbon Nanotubes

Controlling the phase of solid nanoparticles (NPs) is important for adjusting the chirality of single-walled carbon nanotubes (SWCNTs). In spite of three decades of intense research efforts, the mechanism of formation of different phases is still unanswered, even though there is the emergence of metallic carbides with various phases during catalytic growth of SWCNTs. In this work, the mechanism causing the solid NPs with various phases is revealed for the first time by employing the molecular dynamics. The results show that the phase of NPs is closely associated with i) the nucleation intermediate of metallic carbide NPs and ii) the contribution of subsurface C atoms in NPs to the growth of SWCNTs. What's more, according to the transition state theory, the phase of NPs can be tuned by altering the C feeding rate. The findings of the present research open up new prospects for adjusting the phase of solid NPs by controlling the experimental parameters to influence the C feeding rate.