Direct synthesis of suspended single-walled carbon nanotubes crossing plasma sharpened carbon nanofibre tips

Herein we report a method for the direct synthesis of suspended single-walled carbon nanotubes (su-SWNTs) using carbon nanofibres (CNFs) as templates via a three-step fabrication process. Plasma-enhanced chemical vapour deposition was first employed to grow vertically aligned CNFs, which were then post-treated with an energetic argon plasma in the same reactor to yield structural transformation by sharpening tips and reducing embedded catalytic nanoparticles to favourable sizes, presumably below 10 nm. A thermal chemical vapour deposition process subsequently followed, for directly synthesizing SWNTs suspended across the tips or sidewalls of post-treated CNFs (PT-CNFs) with a span up to 10 µm. We also demonstrated that one can maximize the yield of su-SWNTs on the tips of PT-CNFs by optimizing the post-treatment conditions to provide a protective coating which suppresses the growth of SWNTs from sidewalls. In this approach, no further catalyst deposition is needed after the nanostructured PT-CNF template is formed. Thus, su-SWNTs can be selectively positioned on the tips of PT-CNFs with a clean substrate surface free from unwanted CNTs and with a suspension span not limited by the flow conditions of the carbon source gas. This method of fabricating su-SWNTs can be extended to position a single isolated SWNT for the purpose of either minimizing the environmental perturbation during SWNT characterization or enhancing the performance in nanodevice applications.