Supramolecular assembly of single-walled carbon nanotubes at air-solid interface

We formed a stable and reversible Langmuir film (LF) of bundles of unfunctionalized single-walled carbon nanotubes (SWCNTs) at the air-water interface. The film exhibits gas-like and liquid-like phases. The Raman spectrograph of Langmuir-Blodgett (LB) film of single layer of SWCNTs on Si/SiO2 substrate shows the characteristic G, D, and radial breathing mode frequencies of the single-walled carbon nanotubes. Using atomic force microscope (AFM) in spreading resistance imaging mode, we obtained a dependence of target surface pressure on the assembly of SWCNTs in the LB films. The film deposited at very low surface pressure (0.5 mN/m) exhibited an assembly wherein the long axis of the nanotube bundles aligned in the direction of deposition. The LB films deposited in the liquid-like phase of the SWCNTs exhibited supramolecular donut structure. The average width of the SWCNTs was around 30 nm. The current-voltage characterization of the local structures of the LB films using the conducting AFM probe indicates semi-metallic and metallic nature of the donut and the hole in the donut (nanopore), respectively. Such supramolecular assembly of the SWCNTs can find application in the fabrication of the devices like sensors, photochemical cells, batteries, etc.