Bringing Nanotubes to Advanced Electronics

Semiconducting carbon nanotubes could soon make their way into solar panels, printable circuits, stretchable and bendable electronics and inside computer displays, thanks to a new technique developed at Stanford University for increasing the commercial potential this material has.

Carbon nanotubes are already known as being extremely versatile and tough. They can be used for a host of medical, physical and chemical applications, to name but a few. However, they are currently only marginally used in electronic devices, where researchers say they excel.

The reason why that happens is that the CNT manufacturing process itself is not specific to any of the potential applications the finished products are intended for. What this means is that nanotubes which may work for solar cells will not necessary work for transistors, and vice-versa.

Existing technologies produce carbon nanotube powders that contain all sorts of structures. Separating those that are useful for a given application from those that are not is nearly impossible.

Yet, the Stanford team was able to develop a sorting technique that enables single-walled carbon nanotube (SWCNT) to be separated and extracted from conventional nanotube powders. The work was led by associate professor of chemical engineering Zhenan Bao.

Together with colleagues from the University of California in Davis (UCD) and the Samsung Advanced Institute of Technology (SAIT), she and her team published a paper detailing the technique in the latest online issue of the top journal Nature Communications.

“Sorting has been a major bottleneck for carbon nanotubes to be viable for practical electronics applications. This work solves the problem of separating the conducting from the semiconducting nanotubes,” the team leader explains.

She adds that the conducting nanotube component of CNT powders are very useful for creating energy-efficient wires, cables and electrodes, but explains that one of the semiconducting tubes can be used to create stretchable transistors or solar cells.

The secret to the method the team developed is the use of a special polymer, which has an affinity for semiconducting carbon nanotubes alone. What this means is that conducting nanotubes are not bound to the polymer.

By passing the polymer-CNT powder mixture through a solvent solution, the two types of nanotubes are separated, and can then be used for individual, dedicated applications. The Stanford team plans to have the technologies on the market as soon as possible.