Fig. 2

SEM observations of samples A and B. The red rectangles indicate the corresponding magnified areas. The double-headed arrows present the widths of individualized SWCNT gathering areas. The two arrows indicate the coffee rings arising during the drying process of nanotube solution. For sample B, by comparing the contours of coffee rings and SWCNT film in the DEP grooves, we can definitely decide that SWCNT film was formed due to the DEP force induced gathering and alignment but not due to coffee ring effect. The alignment density of individualized SWCNTs on sample B is much higher than that on sample A. The resistances measured betweent the electrodes with aligned SWCNTs are ~20 MΩ for sample A and ~50 KΩ for sample B