Formation of beaded vapor grown carbon nanofibers

Carbon nanofibers having interesting smooth, spherical beads are synthesized using a catalyst assisted vapor phase process under various methane/hydrogen mixtures. Fe(1-x)S(x) powders were used as the catalyst. The synthesis temperatures were 1100 degrees C and 1200 degrees C, which are lower than the ones used previously for the formation of beaded carbon nanofibers or nanotubes. Unlike the high temperature (> or = 1300 degrees C) grown beads that may exhibit a rough surface, all the beads obtained at both 1100 and 1200 degrees C with various methane concentrations have a smooth surface. The diameter and the linear density (no. of beads per unit fiber length) of the beads do not seem to correlate to the growth temperature and the methane concentration. The linear density is also independent of the growth time. However, the beads grow with time. Although the grown mechanism is not clear at the present time, it seems that a three-dimensional nucleation model plays a role.