HANCOCK, N.H. A breakthrough in a joint carbon-nanotube research project, in which carbon nanotubes are chemically sorted based on their electronic properties, may bring electronic applications of nanostructures a step closer.
Creating carbon nanotubes is a fairly easy process, but researchers have been stymied by an inability to sort them out. While geometrically identical, nanotubes come in a many types, based on the spiral structure of their walls, known as chirality.
The problem has been that the chirality-and consequently, the electronic properties-of the tubes can't be distinguished chemically, and chemical reactions are the only way of manipulating them efficiently.
In the new approach pioneered in a project at Rice University (Houston) and the University of Illinois (Urbana), the carbon nanotubes are untangled and dispersed in water using a surfactant. A particular water-soluble salt called diazonium is then added to the mixture. The diazonium bonds to the nanotubes by extracting an electron from them, resulting in an electronically determined chemical reaction.
The next step was finding a reagent that could be attached to the diazonium, which could then serve as a chemical handle. The researchers then applied conventional chemical techniques to sort the tubes according to their handles. In the final step the diazonium and its reagent are removed by heating the solutions.
"Our reaction pathways are based on the electronic properties of the nanotube, not strictly on its geometric structure. This represents a new paradigm in the solution-phase chemistry of carbon nanotubes," said Michael Strano, a professor of chemical and biomolecular engineering at the University of Illinois, who undertook the sorting project in tandem with James Tour, a professor of chemistry, computer science, mechanical engineering and materials science at Rice University.