Vertically aligned carbon nanotubes from premade binary metal oxide nanoparticles on bare SiO2

The synthesis of carbon nanotubes (CNTs) requires well-defined catalyst nanoparticles that can influence both diameter and chirality. Herein, catalyst nanoparticles containing both the catalyst and catalyst support material were developed. Binary-metal oxide (AlO_x–Fe₂O₃) nanoparticles was synthesized from a mixture containing both aluminum and iron oleate precursors in the solution phase. The nanoparticles were assembled as a monolayer film on a silicon oxide (SiO₂) substrate via organic linker molecules to synthesize vertically aligned carbon nanotubes (VA-CNTs). Microscopic and spectroscopic characterization of the premade catalyst nanoparticles and monolayer film assembly revealed the quality of the nanoscale assembly, which facilitated the successful growth of VA-CNTs. The length of the CNTs synthesized using these AlO_x–Fe₂O₃ nanorice catalyst nanoparticles surpassed that of previously reported CNTs grown on bare SiO₂ surfaces without oxide buffer layers. In addition, the CNTs appeared to be directly bonded/connected to the SiO₂ substrate, suggesting CNT formation via the tip-growth mechanism. The effects of growth temperature and catalyst reduction time were evaluated to obtain high-yield VA-CNTs.