Graphene nanoribbons (GNRs), with atomically precise edges, were already known at least theoretically for their highly tunable band gaps. Recent studies have shown that, when cut into thin ribbons just a few atoms wide, graphene obtains a sizable optical band gap (as opposed to full graphene sheets that do not have an optical band gap).
In their experiments, the researchers observed a bright and narrow band emission of red light from individual graphene nanoribbons, only 7-atom-wide, at a high intensity comparable to bright light-emitting devices made from carbon nanotubes. Optical emission was up to 10 million photons per second, about 100 times more intense than the emission measured for previous single-molecular optoelectronic devices, the researchers claim.
In addition, the researchers found that the energy shift of the main peak changes as a function of the voltage, which provides a way to tune the colour of the light. In order to create an electronic-like circuit, the researchers suspended individual GNRs between the tip of a scanning tunnelling microscope (STM) and a gold substrate Au(111), forming an optoelectronic circuit.
According to their calculations, the bright emission involves electronic states localized at the GNR termini. Next, the researchers want to further investigate the impact of defects and GNR aspect ratio (width) on emission, possibly integrating such graphene nanoribbons devices into larger circuitry to create bright, robust, and controllable graphene-based light-emitting devices.
Université de Strasbourg – www.unistra.fr
CNR-Nanoscience Institute – www.nano.cnr.it