The MAXPEEM beamline at the MAX IV Laboratory. Photo: MAX IV Laboratory.
The MAXPEEM beamline at the MAX IV Laboratory. Photo: MAX IV Laboratory.

Two-dimensional sheets of graphene in the form of ribbons a few tens of nanometers across have unique properties that are highly interesting for use in future electronics. Researchers have now, for the first time, fully characterized graphene nanoribbons grown in two possible configurations on the same wafer, and shown that this synthesis process offers a clear route towards upscaling production. The work is described in a paper in ACS Applied Nano Materials.

Graphene in the form of nanoribbons can show so-called ballistic transport, which means that the material does not heat up when a current flows through it. This opens up an interesting path towards high speed, low power nanoelectronics. In a slightly different configuration, however, graphene nanoribbons can behave more like a semiconductor, as found in transistors and diodes.

This is because the properties of graphene nanoribbons are closely related to the precise structure of the edges of the ribbon. The symmetry of the graphene structure lets these edges take two different configurations, termed zig-zag and armchair, depending on the respective directions of the long and short edges of the ribbon.

The researchers from the MAX IV Laboratory at Lund University and Linköping University, both in Sweden, and the Techniche Universität Chemnitz and Leibniz Universität Hannover, both in Germany, grew their nanoribbons on a template made of silicon carbide under well controlled conditions. They then thoroughly characterized the nanoribbons using the MAXPEEM beamline at the MAX IV Laboratory.

The silicon carbide template has ridges running in two different crystallographic directions, which allows both the armchair and zig-zag varieties of graphene nanoribbons to form. The result is the predictable growth of high-quality graphene nanoribbons that have a homogeneity over a millimeter scale and a well-controlled edge structure.

By conducting challenging four probe experiments at a length scale below 100nm, the researchers were able to demonstrate ballistic transport in the bulk of the nanoribbons. The electrical characterization also showed that the resistance is many times higher in the armchair configuration than the zig-zag configuration. This suggests the formation of a band gap in the armchair nanoribbons, making them semiconducting.

The process used for preparing the template for nanoribbon growth is readily scalable and so could form the basis for the large-scale production of graphene nanoribbons, which will be required if they are to become a future material in the electronics industry.

“So far, we have been looking at nanoribbons which are 30–40nm wide,” says Alexei Zakharov at the MAX IV Laboratory. “It's challenging to make nanoribbons that are 10nm or less, but they would have very interesting electrical properties, and there´s a plan to do that. Then we will also study them at the MAXPEEM beamline.”

This story is adapted from material from Lund 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.