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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. Bimetallic aluminum oxide–iron oxide (AlOx–Fe2O3) nanorice 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 AlOx–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. 

Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs.