Schematics bundled SWNTs grown from cobalt clusters on 200 nm silica particle. SWNTs were grown from cobalt particles (black sphere). (a) Small bundle of SWNTs is grown from small size of Co cluster. This growth occurs in sample with 0.2 wt% solution. (b) Large bundle of SWNTs attached to large size of Co cluster. This growth corresponds to the sample with high concentration (0.4 wt%).