Schematic of the tip of a scanning tunneling microscope on a graphene nanoribbon.
Schematic of the tip of a scanning tunneling microscope on a graphene nanoribbon.

Researchers at Aalto University in Finland have succeeded in producing metallic graphene nanoribbons (GNRs) that are only five carbon atoms wide. In an article published in Nature Communications, the researchers report fabricating the GNRs and measuring their electronic structure. Their results suggest that these extremely narrow and single-atom-thick ribbons could be used as metallic interconnects in future microprocessors.

Graphene nanoribbons have been suggested as ideal wires for use in future nanoelectronics. When the size of the wire is reduced to the atomic scale, graphene is expected to outperform copper in terms of conductance and resistance to electromigration, which is the typical breakdown mechanism in thin metallic wires.

However, all the graphene nanoribbons developed so far have been semiconducting, rather than metallic, hampering their use as interconnects. Headed by Peter Liljeroth, researchers from the Atomic Scale Physics and Surface Science groups at Aalto University have now experimentally confirmed that certain atomically-precise graphene nanoribbon widths are nearly metallic, in accordance with earlier predictions based on theoretical calculations.

The team used state-of-the-art scanning tunneling microscopy (STM) that allowed them to probe the graphene nanoribbons’ structure and properties with atomic resolution. “With this technique, we measured the properties of individual ribbons and showed that ribbons longer than 5nm exhibit metallic behavior,” says Amina Kimouche, the lead author of the study.

To produce graphene nanoribbons with precise widths, the researchers developed a novel fabrication process based on chemical reactions on a surface. “The cool thing about the fabrication procedure is that the precursor molecule exactly determines the width of the ribbon. If you want one-carbon-atom-wide ribbons, you simply have to pick a different molecule,” explains Pekka Joensuu, who oversaw the synthesis of the precursor molecules for the ribbons.

The experimental findings were complemented by theoretical calculations by the Quantum Many-Body Physics group headed by Ari Harju. Theory predicts that when the width of the ribbons increases atom-by-atom, every third width should be (nearly) metallic with a very small band gap. “According to quantum mechanics, normally when you make your system smaller, it increases the band gap. Graphene can work differently due to its extraordinary electronic properties,” says Harju’s doctoral student Mikko Ervasti, who performed the calculations.

These results pave the way for using graphene in future electronic devices, where these ultra-narrow ribbons could replace copper as the interconnect material. Future studies will focus on creating all-graphene devices combining both metallic and semiconducting graphene nanostructures. “While we are far from real applications, it is an extremely exciting concept to build useful devices from these tiny structures and to achieve graphene circuits with controlled junctions between GNRs,” says Liljeroth.

This story is adapted from material from Aalto University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.