Graphene ribbons exhibit exceptional electrical conductivity
A team of international researchers has claimed to have created graphene ribbons in which electrons move freely. According to them, charge mobility in the advanced materials exceeded one million cm2/V.s, making their electron mobility 1000 times greater than that of the silicon semiconductors.
The team of scientists from France's Centre National de la Recherche Scientifique (CNRS), Universite de Lorraine, the SOLEIL synchrotron facility, Georgia Institute of Technology, Oak Ridge National laboratory, supported by the Department of Energy, and Universite de Leibniz have devised a novel way of synthesizing graphene ribbons, and have demonstrated their exceptional electrical conductivity at room temperature.
Graphene has excellent electrical conductivity: at room temperature, electrons move through it up to 200 times faster than through silicon and the material's potential in electronics has spurred on a large amount of research worldwide. A collaboration of physicists from France and the US has been studying the electronic properties of graphene since the early 2000s, with a view to designing a material with very high electron mobility at room temperature.
The researchers showed that carbon nanotubes, one of the best-known forms of graphene, can transport electric current ballistically, that is, without encountering resistance within the material. But carbon nanotubes have proved difficult to produce and insert in large quantities onto electronic chips. The researchers have now turned their attention to another form of flat ribbon of graphene. Similarities in electronic structure between carbon nanotubes and graphene ribbons appear to have analogous conductive properties.
The researchers chose to synthesize this 1D graphene from silicon carbide, a commercially available crystal. The scientists claim to have succeeded in obtaining graphene ribbons of high structural quality, made of a narrow sheet of carbon that is 40nm wide. The main challenge was to ensure that the edges of the ribbon remained highly ordered because a graphene ribbon with rough edges does not allow good electron propagation. In order to obtain ribbons with regular edges, the researchers etched nanometer-deep steps into silicon carbide and then produced the graphene ribbons directly on the sidewalls of these steps.
The graphene ribbons produced in this way turned out to be ballistic conductors at room temperature: once inside the material, the electrons moved freely without undergoing any scattering. The ribbons appear to behave as waveguides. Charge mobility in these materials exceeded one million cm2/V.s, which would make their electron mobility 1000 times greater than that of the silicon semiconductors (less than 1700cm2/V.s) used in computer processors and memories. The researchers claimed graphene ribbons are the first to display such conductivity at room temperature.
The ribbons should be able to be produced in large quantities while keeping the same properties. The novel graphene ribbons could find many applications in cutting-edge nanoelectronics.
Conceptual drawing of an electronic circuit comprised of interconnected graphene nanoribbons (black atoms) that are epitaxially grown on steps etched in silicon carbide (yellow atoms). Electrons (blue) travel ballistically along the ribbon and then from one ribbon to the next via the metal contacts. Electron flow is modulated by electrostatic gates. (John Hankinson, Georgia Institute of Technology.)
- Paul Buckley
EE Times Europe