Graphene nanoribbons (GNRs) are unique materials that go from being semiconducting to semimetal as their width increases. They could be used in high-performance nanoelectronics devices, such as field-effect transistors. However, before this becomes possible, researchers need to find a way of routinely making large quantities of high-quality nanoribbons with smooth edges and controllable width. This is because even slightly rough ribbon edges can seriously degrade graphene's properties.

Hongjie Dai and colleagues have now invented a new technique that involves tearing open multiwalled carbon nanotubes to produce GNRs with smooth edges, narrow width distribution and high quality – as revealed by Raman spectroscopy imaging and electrical transport measurements. The MWCNTs (which can be considered as rolled-up GNRs) are unzipped by anisotropic argon plasma etching while covered in a polymer film.

Although there are a number of ways to make GNRs, these methods – which rely either on lithographic patterning, chemical vapour deposition or chemical sonication – produce ribbons that are either too rough or too wide, or have large width distributions or low yield.

The ribbons made by Dai's team have straight edges and are less than around 20 nm wide. Their structure can also be controlled and they show good conductivity and field-effect mobility. That's not all: the unzipping process is compatible with semiconductor processing techniques and few-walled CNTs can be used to obtain sub-10 nm GNRs with band gaps that are large enough for room-temperature transistor applications.

"Compared with previous approaches, ours is more controllable and produces narrow GNRs with narrow width distribution, smooth edges and high quality at a reasonable yield," Dai told "And because aligned CNT arrays can be used to make GNR arrays, it should be possible to produce large-scale, well aligned semiconducting GNRs with controlled structures for practical electronics applications."

The work was reported in Nature.