Cycloaddition Suppresses Nanotube Conductivity

Using a chemical transformation, researchers at DuPont and Cornell University have devised a way to sap metallic single-walled carbon nanotubes (SWNTs) of their conductivity while leaving semiconducting SWNTs unscathed (Science 2009, 323, 234). SWNTs are always produced as a mixture of metallic and semiconducting tubes. Although the semiconducting tubes are promising transistor materials, the metallic tubes short-circuit such devices. The new technique allows scientists to transform bulk quantities of commercial SWNT mats into a material with properties that are suitable for device applications. No tedious separation of the metallic and semiconducting tubes is required. The process, whose development was spearheaded by DuPont's Graciela B. Blanchet, employs a [2+2] cycloaddition of the metallic tubes and a bulky fluorinated olefin. Adding the fluoroolefin to the nanotubes disrupts their π bonding system and thus their conductivity. The fluoroolefins react preferentially with the metallic SWNTs, so by carefully controlling the olefin concentration, the researchers can selectively alter the metallic tubes while leaving the semiconducting tubes unaffected. "This method could offer a viable path for the use of semiconducting carbon nanotubes in commercial electronic devices," according to the researchers.