Length, Bundle, and Density Gradients in Spin Cast Single-Walled Carbon Nanotube Networks
The ability to form single-walled carbon nanotube (SWNT) networks of known density and length distributions is of critical importance to the development of a wide variety of electronic materials that incorporate these molecular wires. Room temperature deposition methods are of great interest as they allow the use of heat-sensitive substrates like polymers and glass. Additionally, they allow greater control over the characteristics of the SWNTs in the network by facilitating physical and/or chemical modification steps prior to deposition. This manuscript describes how two-dimensional networks of SWNTs were formed from aqueous suspensions via spin-casting, a deposition method commonly used in the microelectronics industry due to its ability to deposit uniform thin films of polymers from organic solvents. In the current work, the low viscosity of aqueous suspensions and high spin rates used resulted in ultrathin layers of aqueous suspensions from which low densities of unbundled SWNTs were deposited in iterative deposition cycles. This process was repeated to grow networks exhibiting tunable macroscopic conductivity that could be described by percolation theory.