Successful graphene synthesis out of single molecules
Researchers from the Max Planck Institute for Polymer Research (MPI-P) working with Xinliang Feng and Klaus Müllen succeeded in producing remarkably long, structurally well-defined and liquid-phase-processable graphene nanoribbons (GNRs). This newly developed synthesis method was introduced in the scientific journal "Nature Chemistry". This synthesis method consists in putting together molecular building blocks to produce graphene ribbons in the desired shape and size. The key property of this material is displayed only afterwards: defect-free graphene ribbons show excellent semiconducting properties. As a consequence, this nanomaterial could optimally be used in electronic devices such as transistors and be far more effective than the silicon currently in use. "This is a great step to achieve graphene nanoribbons with unique properties and good solution processability by means of organic solution synthesis" research group leader Feng explains.
A worldwide scientific competition over the research and production of graphene has broken out. The European Commission is thoroughly involved: with a budget of nearly €1 billion over the next ten years, the research program "Graphene Flagship" (2013) provides funding for the utilization of graphene. Scientists at the MPI-P have already made important progresses: since 2003, Klaus Müllen, director at the MPI-P, pursues the "bottom-up" approach to synthesize graphene ribbons from molecular building blocks. Mechanical methods ("top-down") or crystal growth do not reach the necessary precision and produce flawed results. The solution-mediated production method, developed in 2011 by the Müllen's workgroup, meets conversely all the requirements. Thanks to a modification in the method, it is now possible to form structurally well-defined graphene ribbons. Graphene ribbons also have electronic bandgaps, which allow to control the movement of the electrons and the optical properties; a property that graphene - this highly praised wonder material - lacks. As a result, the charge carrier mobility of graphene ribbons is superior to that of silicon.
As a replacement of silicon in electronic devices, batteries or solar cells, graphene ribbons are expected to boost the performance of such devices in the future. Thus, it will be crucial to know if they can be manufactured on an industrial scale with the help of this new solution-synthetized method.
The inherent transdisciplinary cooperation approach of the Institute played a decisive role in this recent research success. The breakthrough made by the synthesis experts was only validated after numerous specific investigations carried by other workgroups of the MPI-P. Laser spectroscopic measurements showed that the graphene obtained in liquid phase has a high photoconductivity. Akimitsu Narita, a PhD student, who was significantly involved in the synthesis, could attest the existence of the bandgaps by investigating the ultraviolet absorption of the solution-synthetized graphene ribbons. Outside the MPI-P, other scientists - from the FU Berlin, the Netherlands, Britain, Denmark and Belgium - were also involved in analyzing the properties of this material.
The material will especially be the object of the fundamental research, to which the MPI-P is committed. The physical properties and their source will be microscopically and spectroscopically investigated to uncover further possible improvements and decisive properties.