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An international research team has produced graphene nanoribbons that can transport electrons without interruption for much greater distances than previous versions, paving the way for more efficient electronic devices.
Graphene has been called a ‘miracle material’ due to its incredible toughness and thinness – so thin, in fact, that it is considered to be two-dimensional. It can also carry electrons with almost no resistance at room temperature – a process known as ballistic transport. If used in computing, it would be at least ten times more efficient than current silicon chips.
But the material lacks a ‘band gap’, which means that, although conductive, it cannot stop electrons and be ‘switched off’, making it impractical for use as a transistor. Scientists have therefore struggled to apply its properties to the electronics field, where it could usher in a new age of ultra-thin, light and flexible computing.
Recent research has focused on graphene nanoribbons of 10 or 20 atoms wide, cut from larger sheets for use in a nano-sized circuit. However, this leaves them with ragged edges, disrupting the flow of electrons. The research by the international research team offers hope that there may be a way round this problem, as well as the switching issue.
The scientists grew the nanoribbons on silicon carbide substrate etched with circuit patterns using standard techniques. The silicone was then heated to 1000°C to melt it off, leaving only the graphene nanoribbons behind, uncut. This allows electrons to move along the edges of the nanoribbons with virtually no resistance, behaving “more like light” according to Walt de Heer, a Regent’s Professor in the School of Physics at the Georgia Institute of Technology who coauthored a report on the findings.
Tests have shown they travel more than 10 micrometres without meeting resistance – 1,000 times farther than in typical graphene nanoribbons. As the electrons don’t scatter, their flow can be interrupted.
“This should enable a new way of doing electronics”, says de Heer. “We are already able to steer these electrons and we can switch them using rudimentary means. We can put a roadblock, and then open it up again. New kinds of switches for this material are now on the horizon.”
Professor Andrea C. Ferrari, Director of the Cambridge Graphene Centre, says that while the results appear to be “a huge step forward” for graphene nanoribbons, “they relate to materials that were created on silicon carbide, so you are limited to this substrate, and don’t have the diamond, plastic or other substrates that you really want to use them on.” – Duncan Jefferies