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\bibitem{He_etal2012} {\textquotedblleft}\textit{Direct evidence for the existence of multi-walled carbon nanotubes with hexagonal cross-sections}{\textquotedblright}. He Z, Ke X, Bals S, Van Tendeloo G, Carbon \textbf{50}, 2524 (2012).   http://doi.org/10.1016/j.carbon.2012.01.075

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