Carbon nanotubes (CNTs) have attracted interest for a wide-range of technological applications including nanoelectronic, energy storage, and energy conversion devices. In many of these applications, the nanotube structure must be sufficiently controlled at the growth stage; however, current growth methods typically produce mixtures of tubes, including multi-walled, single-walled, and a range of different chiralities, that must be purified and separated to facilitate applications.

 

We are interested in controlling the properties of CNTs at the growth stage. We have recently developed a two-step process [1-3] to study and grow CNTs consisting of a microplasma reactor that controls the size- and composition of the nanoparticle catalysts and a flow furnace that nucleates and grows the nanotubes. In addition, the nanotubes are monitored in situ by aerosol measurements to provide real-time feedback and allow the reactor conditions to be rapidly optimized. By tuning the size of our catalyst, we have found that the fraction of single-walled CNTs in the as-grown product can be varied. Similarly, by tuning the composition of the catalyst, we have found that the chirality distribution of the as-grown nanotubes is changed. Here, we will present results for Ni-based bimetallic catalysts and the influence of the catalyst size and composition, as well as other growth parameters such as carbon feedstock and growth temperature, on nanotube growth. In addition to aerosol measurements, the nanotubes are collected and characterized by micro Raman spectroscopy and UV-Vis-NIR absorbance spectroscopy. The structure and properties of the nanotubes and their relationship to the catalyst and other growth parameters will be discussed in detail.

 

1. W-H. Chiang et al., Appl. Phys. Lett. 91, 121503 (2007).

2. W-H. Chiang et al., J. Phys. Chem. C 112, 17920 (2008).

3. W-H. Chiang et al., Nat. Mater. 8, 882 (2009).