Floating evaporative assembly of aligned carbon nanotubes
High density films of semiconducting single-walled carbon nanotubes having a high degree of nanotube alignment are provided. Also provided are methods of making the films and field effect transistors (FETs) that incorporate the films as conducting channel materials. The single-walled carbon nanotubes are deposited from a thin layer of organic solvent containing solubilized single-walled carbon nanotubes that is continuously supplied to the surface of an aqueous medium, inducing evaporative self-assembly upon contacting a solid substrate.
1. A method of forming a film of aligned s-SWCNTs on a substrate, the method comprising:
(a) partially submerging a hydrophobic substrate in an aqueous medium;
(b) supplying a flow of a liquid solution to the aqueous medium, the liquid solution comprising semiconductor-selective-polymer-wrapped s-SWCNTs dispersed in an organic solvent, whereby the liquid solution spreads into a layer on the aqueous medium at an air-liquid interface and semiconductor-selective-polymer-wrapped s-SWCNTs from the layer are deposited as a film of aligned semiconductor-selective-polymer-wrapped s-SWCNTs on the hydrophobic substrate, wherein the organic solvent in the layer, which is evaporating, is resupplied by the flow of the liquid solution during the formation of the film; and
(c) withdrawing the hydrophobic substrate from the aqueous medium, such that the film of aligned semiconductor-selective-polymer-wrapped s-SWCNTs is grown along the length of the hydrophobic substrate as it is withdrawn from the aqueous medium.
2. The method of claim 1 , wherein the organic solvent comprises chloroform.
3. The method of claim 1 , wherein the organic solvent comprises at least one of dichloromethane, N,N-dimethylformamide, benzene, dichlorobenzene, toluene and xylene.
4. The method of claim 1 , further comprising removing the semiconductor-selective polymer from the aligned semiconductor-selective-polymer-wrapped s-SWCNTs.
5. The method of claim 1 , wherein the semiconductor-selective-polymer-wrapped s-SWCNTs in the film have a degree of alignment of about ±20° or better.
6. The method of claim 1 , wherein the single-walled carbon nanotube linear packing density in the film is at least 40 single-walled carbon nanotubes/μm.
7. The method of claim 1 , wherein the substrate is withdrawn at a rate of at least one mm/min.
8. The method of claim 7 , wherein the concentration of s-SWCNTs in the liquid solution is at least 1 μg/mL and the flow of liquid solution is supplied at a rate of at least 160 μL/min.
9. The method of claim 1 , wherein the semiconductor-selective polymer is a polyfluorene derivative.
10. The method of claim 1 , wherein concentration of SWCNTs in the flow of liquid solution is adjusted as it is supplied to the aqueous medium to control the density of s-SWCNTs along the length of the film.