Comparison between Copper and Iron as Catalyst for Chemical Vapor Deposition of Horizontally Aligned Ultralong Single-Walled Carbon Nanotubes on Silicon Substrates

A careful comparison was performed between Cu and Fe as catalysts for the growth of horizontally aligned ultralong single-walled carbon nanotube (SWNT) arrays on SiOx/Si substrates, and the mechanism of the difference was discussed. Cleaner and straighter SWNTs with smaller diameters and narrower size distribution were obtained using Cu as catalyst. It was also found that the SWNTs always grew from the edges of the substrates wherever the catalyst precursors were patterned when Cu was used, while SWNTs normally grew from the patterned catalysts when Fe was used. The size change of Fe and Cu nanoparticles along with the reduction processes shows that Cu nanoparticles were much easier to be vaporized, and the molecular mechanics calculations about the surface energy changes with the particle sizes indicate that the renucleation of Cu tends to form smaller nanoparticles than Fe. This is an important factor that leads to the different performance for Cu and Fe in SWNT growth. This argument was further proved by the fact that using polyvinylpyrrolidone to fix Cu nanoparticles resulted in similar growth behavior to that of Fe catalyst. This study is helpful for further understanding the growth mechanism of SWNTs and gaining more control over the growth of SWNTs.