Ni₃C-assisted growth of carbon nanofibres 300 °C by thermal CVD

Ni-assisted thermal chemical vapor deposition (TCVD) is one of the most common techniques for the growth of carbon nanofibres/nanotubes (CNFs/CNTs). However, some fundamental issues related to the catalytic growth of CNFs/CNTs, such as the low-limit growth temperature, the limiting steps and the state of Ni, are still controversial. Here, we report the growth of CNFs at 300 °C; that is the lowest temperature for the growth of CNFs by TCVD using Ni as the catalyst so far. The results showed that the Ni existed in rhombohedral Ni₃C, not in the normal form of face-centered cubic Ni, and the C atoms for building the CNFs were precipitated from the (001) planes of the faceted Ni₃C nanoparticles. The CNFs are believed to be formed by the decomposition-formation cycle of metastable Ni₃C that has a low-limit decomposition temperature of about 300 °C. Our results strongly suggest that TCVD is a valuable tool for the synthesis of CNFs/CNTs at temperatures below 400 °C, which is generally considered as the upper-limit temperature for fabricating complementary metal oxide semiconductor devices but is the low-limit temperature for growing CNFs/CNTs by TCVD at present. (paper)