Deterministic and preferential synthesis of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are molecular scale wires with diameters of roughly ∼1nm. Their small sizes and unique properties make them promising candidates for future generations of integrated molecular electronics. However, it is well established that SWNTs with different diameters and chiralities have varied electronic structures. To fulfill the exciting potentials of nanotube technology, it is fundamental to develop methodologies for nanotube synthesis with precise control over their structures and assembly. How to obtain homogeneous nanotube materials with-specific physical properties and then to assemble them into desired architectures are pressing issues actively sought after in both academia and industry.; My work focused on controlled and preferential synthesis of SWNTs by chemical vapor deposition (CVD). First we developed a novel catalyst, based on an iron-containing protein ferritin, to grow nanotubes. By varying the number of iron atoms stored in each ferritin, we obtained catalytic iron oxide nanoparticles with specific sizes. These particles with narrow size distributions enabled us to grow SWNTs with controlled diameter. We then demonstrated that by applying an external electrical field during CVD synthesis, we could control the orientations of the SWNTs. The first directly grown ordered nanotube architectures and networks, either suspended or lying on the surface, were achieved. Finally we presented low temperature synthesis of high quality SWNTs by a remote plasma enhanced CVD (PECVD) method. We found this PECVD method could preferentially grow semiconducting SWNTs (s-SWNTs) at a high percentage of ∼90%. Systematic experimental study revealed a strong correlation between s-SWNTs percentage and their diameter distribution. Theoretical calculations showed that SWNTs of different electrical properties exhibit discernable differences in the heat of formation energies. S-SWNTs have the lower energies and are more stable than metallic/quasi-metallic SWNTs. We suggest a thermodynamic factor could be responsible for the preferential synthesis. This work shows promising improvements achieved towards the ultimate goal of controlled SWNT synthesis: directly grown complex and organized structures composed of SWNTs with the same chirality.