A fabrication technique of high-purity vertically aligned single-walled carbon nanotubes (VA-SWCNTs) using atmospheric pressure plasma enhanced chemical vapor deposition is presented. Although densely mono-dispersed Fe-Co catalysts of a few nanometers is primarily responsible for VA-SWCNT growth, carbon precipitation was virtually absent in the thermal CVD regime at 700 °C. On the other hand, high-purity VA-SWCNTs without measurable defects were grown at 4 μm min-1 by applying atmospheric pressure radio-frequency discharge (APRFD) which has been previously developed for this purpose. The results proved that cathodic ion sheath adjacent to the substrates, where a large potential drop exists, also plays an essential role for the controlled growth of SWCNTs, while ion damage to the VA-SWCNTs is inherently avoided due to high collision frequency among molecules in atmospheric pressure. Operation regime of APRFD and tentative reaction mechanisms for VA-SWCNT growth are discussed along with optical emission spectroscopy of near substrate region.
Bibliographical noteFunding Information:
This project was partly supported by the Grants-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 18686018). We would like to thank Professor Joachim Heberlein, Department of Mechanical Engineering of The University of Minnesota, for the collaborative development of atmospheric pressure radio-frequency discharge. T.N. would like to thank Professor Shigeo Maruyama, Department of Mechanical Engineering of The University of Tokyo, for the valuable discussion about catalyst preparation and SWCNT characterization. Mr. Akira Genseki, Center for Advanced Materials Analysis of Tokyo Institute of Technology, supported TEM analysis.