Aromatic graphene

To date, graphene has been produced, for example, by depositing carbon atoms from the gas phase or by thermal graphitization of silicon carbide. In contrast to this, the cooperation project led by Bielefeld University and involving PTB and Ulm University chose to start from aromatic molecules. As substrates, both copper single-crystals and inexpensive polycrystalline copper foils were used. By irradiation with low-energy electrons and subsequent thermal annealing, it was then possible to convert a self-organized single-layer of the molecule biphenyl thiol, which had precipitated on the copper surface, into graphene.

To investigate the chemical and physical properties of the graphene manufactured in this way, different characterization methods from Ulm and Bielefeld Universities and from PTB were applied such as, for example, scanning tunnelling microscopy, transmission electron microscopy, Raman spectroscopy as well as electric transport measurements at low temperatures and high magnetic fields. All these measurements confirmed that graphene of excellent crystalline and electronic quality had actually been manufactured from the aromatic molecule.

The flexibility of the electron irradiation, which is possible with very good spatial resolution, now allows graphene structures of basically any form to be manufactured, e.g. quantum dots, nanoribbons or other nano-geometries with specific functionality. The selection of the temperature in the thermal conversion step also allows the degree of crystallinity and the characteristics of the graphene depending on it to be adjusted.

Additional advantages result from the versatility of the method of selforganized coating. It can be performed with different aromatic molecules which could, for example, also contain doping atoms for electronic doping of the final product. Applied in multiple layers, socalled bi-layer or multi-layer graphene could be manufactured, whose changed electronic band structure would expand the potential applications of single-layer graphene. Likewise, other substrates than the copper used here (for example, other metals, semiconductors, isolators) could be used. In addition, it should also be possible to manufacture graphene on any three-dimensional surfaces, as molecular self-organization also takes place on curved surfaces. The new production method considerably broadens the perspectives for the utilization of the “magical material”.