WILMINGTON, DE/ITHACA, NY - Scientists at DuPont and Cornell University have used a simple chemical process to convert “as grown” mixtures of metallic and semiconducting carbon nanotubes into solely semiconducting carbon nanotubes with electrical characteristics well suited for plastic electronics. This new finding, reported in the January 9 issue of the journal Science, identifies a commercially viable path for the production of bulk quantities of organic semiconducting ink, which can be printed into thin, flexible electronics such as transistors and photovoltaic materials for solar cell technology.
The study was authored by DuPont Research Fellow Graciela B. Blanchet, Cornell University Associate Professor of Materials Science and Engineering George Malliaras, former Cornell Post-Doctoral Fellow Mandakini Kanungo and DuPont Research Chemist Helen Lu under the title, “Suppression of Metallic Conductivity of Single-Walled Carbon Nanotubes by Cycloaddition Reactions.” The research was funded by a U.S. Air Force grant to Cornell University.
Since their discovery in the early 1990s, there has been great interest in the revolutionary electrical, mechanical and thermal properties of carbon nanotubes. However, the fact that carbon nanotubes are produced as complex mixtures can greatly limit their applications. In 2003, DuPont scientists published in Science a method to separate carbon nanotubes using DNA. DuPont has continued to investigate these materials. The current development is a significant advancement in this pioneering field and is a more promising approach to developing semiconductor applications of carbon nanotubes.
“A significant limitation in electronic application of carbon nanotubes has been the difficulty in separating metallic from semiconducting carbon nanotubes,” Blanchet said. “Our research uncovered a potentially low-cost route to suppress the conductivity of the metallic tubes without requiring further separation of nanotubes by type.”
“We are looking forward to exploring the use of this material in a wide range of devices for applications such as novel organic photovoltaic structures,” Malliaras said.
In an example that illustrates the effectiveness of industrial and academic collaborations, the group has developed a simple chemical process that brought fluorine-based molecules into contact with the nanotubes. Through a process called cycloaddition, the fluorine molecules efficiently attacked or converted the metallic nanotubes, leaving the semiconducting tubes alone, and creating a perfect batch of solely semiconducting nanotubes. The resulting carbon nanotubes were dispersed into semiconducting ink and used in thin film transistors that are designed to be thinner, lighter and use less energy.
“It appears that cycloaddition, as opposed to the standard monovalent attachment of molecules, provides an effective method for suppressing the conductivity of the metallic nanotubes in a very controlled fashion,” Blanchet said. “Our work suggests that careful control of the chemical reaction enables the suppression of metallic tubes without degradation of semiconducting tubes.”
