These seeds could potentially be placed in specific locations on a computer chip using an existing chemical method, Tour says. Nanotubes with selected electronic properties could then be grown exactly where they are needed.
The Rice method is an outgrowth of research by the late Richard Smalley, who received the Nobel Prize in 1996 for discovering buckyballs, or fullerenes, and pioneered much of today’s work on carbon nanotubes. Smalley, who died just over a year ago, is the first author on the paper.
Many other researchers are developing methods for eliminating unwanted nanotubes from a batch by using ultracentrifuges or electric fields to sort them or by etching them away (see “Nanotube Computing Breakthrough” and “A Step Closer to Nanotube Computers”). These methods, however, aren’t as selective as the iron particle-carbon nanotube seeding technique being developed at Rice.
The main issue with the Rice method is yield. In the current research, only about 3 percent of the chopped up nanotubes grew larger. Tour hopes to improve yield by adjusting the fit between the size of the iron nanoparticles used as catalysts and the diameter of the nanotubes being grown.
The researchers also need to demonstrate that the process can work with a variety of nanotube types and grow nanotubes on a much larger scale, Strano says.
If these obstacles can be overcome, the new method could be a boon to engineers and scientists alike. The variation among nanotubes is so great that there’s “almost a new periodic table of nanotube types,” Strano says. “If [the Rice method] works, it will really enable the field.”