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\bibitem{Zhang_etal1993} {\textquotedblleft}\textit{Carbon nano-tubes: their formation process and observation by electron microscopy}{\textquotedblright}. Zhang XF, Zhang XB, Van Tendeloo G, Amelinckx S, op de Beeck M, van Landuyt J, Journal of crystal growth \textbf{130}, 368 (1993).   http://doi.org/10.1016/0022-0248(93)90522-X

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