"Confinement changes graphene's behaviour," said physicist An-Ping Li. Graphene in sheets is an electrical conductor, but narrowing graphene can turn the material into a semiconductor if the ribbons are made with a specific edge shape.
To grow graphene nanoribbons with controlled width and edge structure from polymer precursors, previous researchers had used a metal substrate to catalyse a chemical reaction. However, the metal substrate suppresses useful edge states and shrinks the desired band gap.
The team claim to be the first to grow graphene nanoribbons without a metal substrate. Instead, they injected charge carriers that promote a chemical reaction that converts a polymer precursor into a graphene nanoribbon.
At selected sites, the technique can create interfaces between materials with different electronic properties. These interfaces are said to be the basis of semiconductor electronic devices.
"When graphene becomes narrow, it creates an energy gap," Li said. "The narrower the ribbon is, the wider is the energy gap."
According to the researchers, the technique could provide the basis for an electronic device that could carry current with virtually no resistance, even at room temperature.
"It's a way to tailor physical properties for energy applications," Li said. "This is an excellent example of direct writing. You can direct the transformation process at the molecular or atomic level." Plus, the process could be scaled up and automated.
