Researchers at Shanghai Jiao Tong University, Stanford University, and other US and China institutes have designed a strategy for creating graphene nanoribbons (GNRs) with smooth edges that are below 10 nm in width. This new method is based on the use of squashed carbon nanotubes (CNTs).

The team explained that the idea behind this new work is that if carbon nanotubes (CNTs) can be squashed into GNRs, it would be possible to produce narrow (sub-5-nm wide) GNRs from CNTs that have small diameters. The team said that the GNRs prepared using this method would be much narrower than those obtained by previous methods.

Another goal of this recent collaboration was to achieve atomically smooth edges throughout the whole GNRs, by forming edge-closed GNRs that exhibited high material and device mobility. To produce their sub-10-nm-wide and long GNRs with atomically smooth closed edges, the researchers squashed CNTs together using the high-pressure and thermal treatment method they devised.

"We used a DAC for the high-pressure treatment of CNTs," the researchers explained. "The CNT samples were sealed in a sample chamber in the DAC and then were compressed between the tips of two diamond anvils. To stabilize the squashed sample structure, we conducted a thermal treatment on the sample while it was at high pressure."

The created GNRs reportedly have atomically smooth, closed edges and very few defects. Using the method they devised, the team was even able to produce sub-5-nm GNRs with a minimum width of 1.4 nm. Remarkably, they found that a field effect transistor (FET) based on a 2.8-nm-wide edge-closed GNR exhibited a high Ion/Ioff ratio of >104, field-effect mobility of 2,443 cm2 V−1 s−1 and on-state channel conductivity of 7.42 mS.

"Our research proves that sub-10-nm-wide semiconducting graphene nanoribbons with atomically smooth closed edges can be produced by squashing carbon nanotubes using a combined high-pressure and thermal treatment," the team said. "With this approach, nanoribbons as narrow as 1.4 nm can be created. The edge-opened nanoribbons were also fabricated using nitric acid as the oxidant to selectively etch the edges of the squashed nanotubes under high pressure."

The study could have important implications for the development of new electronic and optoelectronic devices. In the future, the method could be used to produce high-quality, narrow, and long semiconducting GNRs.

In addition, the fabrication strategy allows engineers to control a GNR's edge types. This could help to explore the fundamental properties and practical applications of GNRs in electronics and optoelectronics further. Ultimately, the method developed could also be adapted to synthesize other desirable materials-based nanoribbons using squashed nanotubes or to flatten other fullerene materials.