Large-area fluidic assembly of single-walled carbon nanotubes through dip-coating and directional evaporation

We present a simple and scalable fluidic-assembly approach, in which bundles of single-walled carbon nanotubes (SWCNTs) are selectively aligned and deposited by directionally controlled dip-coating and solvent evaporation processes. The patterned surface with alternating regions of hydrophobic polydimethyl siloxane (PDMS) (height ~ 100 nm) strips and hydrophilic SiO₂ substrate was withdrawn vertically at a constant speed (~3 mm/min) from a solution bath containing SWCNTs (~0.1 mg/ml), allowing for directional evaporation and subsequent selective deposition of nanotube bundles along the edges of horizontally aligned PDMS strips. In addition, the fluidic assembly was applied to fabricate a field effect transistor (FET) with highly oriented SWCNTs, which demonstrate significantly higher current density as well as high turn-off ratio (T/O ratio ~ 100) as compared to that with randomly distributed carbon nanotube bundles (T/O ratio ~ <10).