Making High-Quality, Lower-Cost Transistors for Flexible Electronics Published May 7, 2009 By Maria Callier AFOSR ARLINGTON, Va. -- A team composed of researchers from DuPont and Cornell University has found a way to separate metallic and semiconducting carbon nanotubes, a discovery with potential advantages in the creation of transistors--specifically, those designed for flexible electronics applications. The AFRL-funded scientists uncovered a means of producing large amounts of organic semiconducting ink that can, in turn, be transformed into thin, flexible electronic devices. Leveraging DuPont's unique expertise in fluorine chemistry and Cornell's sophisticated knowledge of device fabrication, the scientists were able to tailor the conversion of metallic nanotubes and the simultaneous exfoliation of the nanotube ropes. These converted tubes may ultimately facilitate the manufacture of high-quality, lower-cost printable electronics. Though recognized years ago as viable--even revolutionary--in the field of electronics, metallic tubes were known culprits in shorting transistor current paths. This deficiency prompted scientists to explore feasible methods of achieving separation. Whereas initial investigations revealed that DNA could separate the metallic tubes from the semiconductors, the lab-sponsored team's results show that attaching fluorinated molecules to nanotube walls can produce the same result. It is unclear whether the connection between two of the tube's carbon atoms to two of the reactant molecule's carbon atoms "kills" the metallic tubes or merely converts them to semiconductors. Either way, the huge reduction in metallic tubes prevents electrical shorts in the transistors and requires no further separation of nanotubes by type. The researchers' next steps are to focus on testing the semiconducting tubes in a variety of electronic devices and scaling up ink manufacturing. This work is a real breakthrough and will benefit many organic materials and devices, such as solar cells and photodetectors, wherein charge mobility is a limiting factor in performance.