Template-Free Directional Growth of Single-Walled Carbon Nanotubes on a- And r-Plane Sapphire

Sapphire is a material of a unique combination of physical, chemical and optical properties, which make it resistant to high temperature, thermal shock, water and sand erosion, and scratching. It is a superior window material for many IR applications from 3µm to 5µm. C-plane sapphire substrates are widely used to grow III-V and II-VI compounds such as GaN for blue LED and laser diodes, while R-plane sapphire substrates are used for the hetero-epitaxial deposition of silicon for microelectronic IC applications.

We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plane and r-plane sapphire substrates. This is achieved using chemical vapor deposition with ferritin as the catalyst. The nanotubes are aligned normal to the direction for growth on the a-plane sapphire. They are typically tens of micrometers long, with a narrow diameter distribution of 1.34 ± 0.30 nm. In contrast, no orientation was achieved for growth on the c-plane and m-plane sapphire, or when Fe films, instead of ferritin, were used as the catalyst. Such orientation control is likely related to the interaction between carbon nanotubes and the sapphire substrate, which is supported by the observation that when a second layer of nanotubes was grown, they followed the gas flow direction. These aligned nanotube arrays may enable the construction of integrable and scalable nanotube devices and systems.


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