Posted: January 8, 2009

Novel process to make high-performance carbon nanotube inks

(Nanowerk News) 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 (Vol. 323 No. 234) 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."
Blanchet received her master's degree in physics from the University of Buenos Aires, Argentina and Ph.D. in physics from Brown University. At DuPont she has pioneered the areas of digital proofing, digital color filters and printable electronics. She holds approximately 70 patents in the fields of organic electronics, laser ablation, high temperature superconductors and organic conducting and semiconducting composites. In 2005, her team was recognized in the Scientific American 50 for their work in nanotube based flexible electronics.
Lu holds 18 patents in the field of catalysis, polymers for coating, carbon nanotube materials and biomedical polymers. She is a graduate of Cornell University (undergraduate) and Yale University (Ph.D.).
DuPont Science & Technology provides technologies and transformational options for new and existing businesses, building on a long, rich legacy of leading-edge science and innovation. Products commercialized over the last five years accounted for 36 percent of the company's total revenue.
DuPont is a science-based products and services company. Founded in 1802, DuPont puts science to work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere. Operating in more than 70 countries, DuPont offers a wide range of innovative products and services for markets including agriculture and food; building and construction; communications; and transportation.
Source: DuPont; Cornell University
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