Schematic of the
tip of a scanning tunneling microscope on a graphene nanoribbon.
Picture: Peter
Liljeroth's team.
(December 15, 2015) Researchers at Aalto University have
succeeded in experimentally realizing metallic graphene nanoribbons that are
only 5 carbon atoms wide.
The results suggest that these extremely narrow and
single-atom-thick ribbons could be used as metallic interconnects in future
microprocessors. In their article published in Nature Communications, the
research team demonstrated fabrication of the graphene nanoribbons (GNR) and
measured their electronic structure.
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 demonstrated graphene nanoribbons have been
semiconducting, which hampers their use as interconnects. Headed by Prof. Peter
Liljeroth, researchers from the Atomic Scale Physics and Surface Science groups
have now shown experimentally 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 allows them to probe the material’s structure and properties with
atomic resolution.
– With this technique, we measured the properties of
individual ribbons and showed that ribbons longer than 5 nanometers exhibit
metallic behaviour, says Dr Amina Kimouche, the lead author of the study.
The nanoribbon fabrication is based on a chemical reaction
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 Dr 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 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 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.