Manufacturing Aligned Arrays of Semiconducting Carbon Nanotubes for Faster and More Energy Efficient Next-Generation Electronics

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Carbon nanotubes are nanomaterials that are comprised entirely of carbon atoms arranged in a cylinder. The diameter of a carbon nanotube is only about 1 nanometer or 1 billionth of a meter. Carbon nanotubes are among the best conductors of electricity that have ever been discovered. They promise to increase the speed and complexity of computing devices, increase the bandwidth and energy efficiency of commercial and military wireless communications technologies, and lead to new types of unconventional electronics that are not rigid but can be stretched, rolled, and folded. To realize nanotubes' promise, researchers must first learn how to assemble them into aligned arrays on substrates. This award supports fundamental research on a recently discovered manufacturing process for achieving this goal. Inks containing semiconducting carbon nanotubes are spread into thin films on the surface of a water trough. The nanotubes deposit and align themselves on a substrate as it is withdrawn from the trough. The overarching objective of the research is to increase the uniformity and improve the organization of the nanotube arrays to open the door for large-area nanotube array manufacturing for commercial applications. These advances will benefit the U.S. economy, high-tech electronics industries, and society. Moreover, the efforts on nanomaterials metrology and manufacturing will impact the development of new undergraduate laboratories on materials characterization for engineering education.The nanotube assembly occurs via a process called floating evaporative self-assembly. The uniformity and organization of nanotubes will be improved by: (1) determining the mechanisms that direct nanotube organization during floating evaporative self-assembly; (2) controlling packing density and inter-nanotube spacing by using multifunctional polymers to wrap the nanotubes and mediate inter-nanotube interactions during assembly; and (3) developing metrology to understand the link between processing-structure-electrical properties. In preliminary research, floating evaporative self-assembly has been exploited to align arrays of ultrahigh purity semiconducting nanotubes prepared using conjugated polymers as nanotube-differentiating agents. The excellent degree of alignment and control over the packing density of the nanotubes using this method has led to gains in nanotube array field effect transistor performance of 1400x in on/off ratio (at constant conductance) and 30-100x in on-conductance (at constant on/off ratio). Increasing the uniformity of these arrays will open the door for commercial opportunities in thin film applications and macroelectronics. Further controlling the microstructure will open the door for increased conductance and commercial opportunities in high-frequency linear amplifiers and logic transistors.