With Co-Cu binary catalyst, a novel combination recently proposed, we are able to synthesize vertically aligned (VA-) SWNTs with diameter tunable down to 1 nm, which is so far smallest for VA-SWNT arrays. Chirality selective growth of SWNTs achieved in ACCVD from sputtered Co-W catalyst. This sputtered Co-W catalyst is able to grow SWNTs uniformly on entire substrate with a (12,6) enrichment of 70%.
To clarify to growth mechanism in binary catalyst, we propose an in-plane TEM approach, which enables a direct characterization of catalyst particles with atomic resolutions on a MEMS-fabricated thin SiO2 film. Since no transfer or any post treatments are needed, the most original morphology is preserved. By this technique we confirm that, with the addition of Cu, much smaller Co particles form epitaxially on Cu and produce all sub-nm vertically aligned SWNTs. In Co-W, selective area electron diffraction (SAED) suggests an intermediate Co6W6C structure that is possibly associated with growth selectivity. High-angle annular dark-field imaging (HAADF) reveals the the junction between metallic W and Co-W.
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This work was supported by JSPS KAKENHI Grant Numbers JP25107002, JP15H05760, JP15K17984, and IRENA Project by JST-EC DG RTD, Strategic International Collaborative Research Program, SICORP. Part of this work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). We also acknowledge supports from Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.