Researchers can grow samples containing mostly metallic carbon nanotubes by carefully controlling the ambient gases used during production.
Single-walled carbon nanotubes are usually grown in mixtures that are one-third metallic and two-thirds semiconducting. However, applications in electronics require samples with well-defined electronic properties. Now, Avetik Harutyunyan and co-workers at the Honda Research Institute USA, the University of Louisville and Purdue University have shown that the gases used during the growth process can have a strong influence on the type of nanotubes that are synthezied1.
The researchers grew single-walled carbon nanotubes using iron nanoparticles as catalysts and methane as a carbon source in various different ambient gas atmospheres. They found that an atmosphere of helium and water was preferential for producing metallic nanotubes, whereas argon and water produced more semiconducting nanotubes. The gases seemed to affect the iron nanoparticles in different ways: helium made the nanoparticles swell up and take on a shape with flat sides and sharp corners, whereas argon made the particles more rounded.
Harutyunyan and co-workers produced samples in which up to 91% of the nanotubes were metallic, raising hopes that it will soon be possible to grow pure batches of nanotubes for specific applications.
References
Harutyunyan, A. R. et al. Preferential growth of single-walled carbon nanotubes with metallic conductivity. Science 326, 116–120 (2009).
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Reid, T. Creating the right atmosphere. Nature Nanotech (2009). https://doi.org/10.1038/nnano.2009.335
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DOI: https://doi.org/10.1038/nnano.2009.335