A big barrier to building useful electronics with carbon nanotubes has always been the fact that when they’re arrayed into films, a certain portion of them will act more like metals than semiconductors.
Now researchers from the University of Illinois-Urbana Champaign have shown how to strip out the metallic carbon nanotubes from arrays using a relatively simple, scalable procedure that does not require expensive equipment.
Using the new technique, the researchers were able to deposit a thin coating of organic material directly on top of a sheet of arrayed nanotubes in contact with a sheet of metal. They then applied a current to the sheet, which allowed the current to flow through the nanotubes that were metal conductors, but not the bulk of the tubes, which were semiconducting.
The current heated up the metal nanotubes to create a thermal capillary flow that opened up a trench in the organic topcoat above them. Unprotected, the metallic tubes could then be etched away using a standard benchtop instrument, and the organic topcoat could be washed away. This left an electronic wafer coated with semiconducting nanotubes free of metallic contaminants. The researchers successfully tested this method by building arrays of transistors.