Various methods of CNT film preparation. a, CVD-grown aligned individual SWCNTs on SiO2 substrate using stable and laminar gas flow. b, Aligned array of CNTs on ST-cut quartz with narrow strip pattern of Fe catalyst. Reproduced with permission . Copyright 2007, Nature Publishing Group. c, Array of vertically aligned MWCNTs on Fe/Al/SiO2 substrate. d, Random network SWCNTs prepared by spray of CNT solution (left) and CVD-grown on SiO2 substrate (right). e, Yarning of vertically aligned MWCNT film.