Researchers at Aalto University in Finland, have experimentally realized metallic graphene nanoribbons that are 5 carbon atoms wide. They say their work could pave the way for using graphene in future electronic devices, where it could replace copper as the interconnect material. Graphene nanoribbons have already 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 demonstrated graphene nanoribbons have been semiconducting, which hampers their use as interconnects.

Headed by Peter Liljeroth, professor of physics, researchers from the Atomic Scale Physics and Surface Science groups have shown that certain atomically precise graphene nanoribbon widths are nearly metallic, in accordance with earlier predictions based on theoretical calculations. The team used scanning tunneling microscopy (STM) which allowed them to probe the material’s structure and properties with atomic resolution. With this technique, the properties of individual ribbons were measured. The technique showed that ribbons longer than 5 nanometers exhibit metallic behavior.

Scanning tunneling microscopy revealed that ribbons longer than 5 nanometers exhibit metallic behavior.Scanning tunneling microscopy revealed that ribbons longer than 5 nanometers exhibit metallic behavior. "The cool thing about the [nanoribbon] fabrication procedure is that the precursor molecule exactly determines the width of the ribbon," says Dr. Pekka Joensuu, who oversaw the synthesis of the precursor molecules for the ribbons. "If you want one-carbon-atom-wide ribbons, you simply have to pick a different molecule."

The findings were complemented by theoretical calculations by the Quantum Many-Body Physics group, headed by Dr. Ari Harju. The theory predicts that when the width of the ribbons is increased atom by atom, every third width should be (nearly) metallic with a small band gap.

According to quantum mechanics, when a system is made smaller, it normally increases the band gap. Graphene can work differently due to its extraordinary electronic properties, says Harju's doctoral student, Mikko Ervasti.

Future studies will focus on all-graphene devices that combine both metallic and semiconducting graphene nanostructures.

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