Cap Formation Engineering: From Opened C₆₀ to Single-Walled Carbon Nanotubes

Abstract

Structural control, and especially chirality control, remains a significant challenge in the synthesis of single-walled carbon nanotubes (SWNTs). We report herein a rational approach to engineering fullerene caps for growing SWNTs with controlled structures via chemical vapor deposition (CVD). Opening of fullerendione via thermal oxidation yields hemispherical caps which can initiate SWNT growth at their open ends. The size and structure of these caps can be engineered by tuning the temperature of thermal oxidation. Results show that pregrowth treatment of the cap is indispensable to successful growth of SWNTs. The temperature used for thermal oxidation strongly affects the size and structure of the cap and further determines the diameter distribution of the as-grown SWNTs. Stronger oxidation treatments (450 degrees C oxidation in air) promote formation of thinner SWNTs, while weaker oxidation treatments (350 degrees C oxidation in air) lead to wider SWNTs. Interestingly, SWNTs made using fullerene caps show steplike diameter distributions relative to SWNTs catalyzed by Fe nanoparticles. This cap engineering using opened C(60) provides a potential approach to grow SWNTs with controlled structures.

Design and Synthesis of Carbon Nanotube Segments

“…Liu and co-workers reported am etal-free synthesis of CNTs by using af ullerene cap (Scheme 44), [81] whereby fullerenedione 172,synthesized in three steps from C 60 , [82] was thermally decomposed and subsequently used as at emplate for CNT growth without purification. Thed iameter distribution of the resulting CNTs was found to be affected by the temperature of the thermal decomposition step (300-500 8 8C in air), which was explained by the conversion of the fullerenedione 172 into end-cap structures of various sizes, whereby the size was argued to depend on the reaction conditions.A ccordingly,n ot only the theoretically expected (5,5)CNT was formed, but also CNTs with other diameters.…”

Synthesis of carbon nanotubes with and without catalyst particles

“…Exciting strategies to open fullerenes and use them as nucleation caps for SWNT have also been demonstrated. Once the fullerenes have been opened they are subjected to a CVD process and grow tubes [49,50]. The proposed growth mechanism is given in Figure 6.…”

“…In this scenario, carbon species are able to diffuse along the surface of graphitic layers which are then adsorbed at the edges. This self-assembling mechanism can explain the growth of cloned SWNT [51], SWNT nucleated from opened fullerenes [49,50] and from MWNT grown on graphitic surfaces [52,53]. In the case of CNT growth from stable oxides (oxides which are not reduced in the reaction), either in nano-particulate form or as the support material, the VLS theory is not valid since carbon dissolution is unlikely and probably occurs through surface diffusion processes.…”

Catalytic Consequence of the Interface Between Iron Catalysts and Foils in Synthesis of Aligned Nanocarbons on Foils

“…Transition metals are normally required to grow CNTs, and the growth mechanism of the CNTs on the transition metal nanoparticles has been studied intensively. There is prevalent CNT growth mechanism involving surface reactions leading to surface carbon, segregation and dissolution of the surface carbon into the metallic particles, diffusion of carbon and formation and precipitation of the graphene layers [36][37][38]. At high growth temperatures, both the small size and the relatively high concentration of carbon in metal-carbon solid solution make the metal nanoparticles mobile and appearing liquid-like particles.…”