Growth of Ultrahigh Density Single-Walled Carbon Nanotube Forests by Improved Catalyst Design

We have grown vertically aligned single-walled carbon nanotube forests with an area density of 1.5 × 10¹³ cm^–2, the highest yet achieved, by reducing the average diameter of the nanotubes. We use a nanolaminate Fe–Al₂O₃ catalyst design consisting of three layers of Al₂O₃, Fe, and Al₂O₃, in which the lower Al₂O₃ layer is densified by an oxygen plasma treatment to increase its diffusion barrier properties, to allow a thinner catalyst layer to be used. This high nanotube density is desirable for using carbon nanotubes as interconnects in integrated circuits

Effect of Catalyst Pretreatment on Chirality-Selective Growth of Single-Walled Carbon Nanotubes

We show that catalyst pretreatment conditions can have a profound effect on the chiral distribution in single-walled carbon nanotube chemical vapor deposition. Using a SiO₂-supported cobalt model catalyst and pretreatment in NH₃, we obtain a comparably narrowed chiral distribution with a downshifted tube diameter range, independent of the hydrocarbon source. Our findings demonstrate that the state of the catalyst at the point of carbon nanotube nucleation is of fundamental importance for chiral control, thus identifying the pretreatment atmosphere as a key parameter for control of diameter and chirality distributions

Co-Catalytic Solid-State Reduction Applied to Carbon Nanotube Growth

We report on a new class of cocatalysts for the chemical vapor deposition of carbon nanotubes, where the cocomponent (Ta) acts as a solid-state reducing agent for the active catalyst (Fe). The cocatalytic FeTa system enables carbon nanotube growth without the need for a reducing gas atmosphere such as H2 or NH3. In situ X-ray photoelectron spectroscopy reveals that the tantalum (oxide) getters the oxygen from the iron (oxide) by a diffusive solid-state process, driven by the much larger affinity to oxygen of Ta compared to Fe. We suggest that this redox-based mechanism is applicable to a wide range of metal (oxide)/catalyst systems and relevant to rational catalyst design in general heterogeneous catalysis