Graphene and graphene nanostructures

Graphene, an atomically thin, two-dimensional sheet of carbon atoms arranged in a hexagonal honeycomb lattice exhibits unique electronic and structural properties and is one of the most intensively studied material systems nowadays. Its linear energy dispersion gives rise to extremely high electron mobilities, making graphene an ideal candidate for high performance electronic applications.
We grow graphene epitaxially on silicon carbide (SiC) substrates, a very promising way of producing graphene especially for the purpose of electronic applications. The electronic structure of epitaxial graphene can be modified for specific applications by tailoring the SiC/graphene interface.The graphene layers are extensively characterized, with respect to electronic (e.g. doping) and structural properties (e.g. defects). The local transport properties are studied by means of a 4-tip STM, which allows us to measure the conductance with probe spacings as small as 100 nm.

Further research is dedicated to the patterning of graphene into small stripes, the so called graphene nanoribbons. The electronic confinement in these structures gives rise to exciting alterations of the band structure. Depending on the edge orientation ballistic edge channels can be generated if the edges of the ribbons are almost defect free. We use a selective graphitization process on SiC mesa structures to grow graphene nanostructures directly in the desired shape to avoid any damaging post-processing. The graphene nanoribbons produced with this method exhibit exceptional tranpsort properties, such as ballistic conduction even at room temperature with mean free paths up to several µm.

AFM and SEM image of graphene nanoribbons grown on SiC mesa sidewalls




SEM image of four probes contacting a graphene nanoribbon

Selected publications:

J. Baringhaus, J. Aprojanz, J. Wiegand, D. Laube, M. Halbauer, J. Hübner, M. Oestreich and C. Tegenkamp (2015): Growth and characterization of sidewall graphene nanoribbons, Appl. Phys. Lett. 106, 043109 (2015)  
DOI: 10.1063/1.4907041

Jens Baringhaus, Alexander Stöhr, Stiven Forti, Ulrich Starke amd Christoph Tegenkamp (2015): Ballistic bipolar junctions in chemically gated graphene ribbons, Sci. Rep. 5, 9955, (2015)  
DOI: 10.1038/srep09955

Jens Baringhaus, Ming Ruan, Frederik Edler, Antonio Tejeda, Muriel Sicot, Amina Taleb-Ibrahimi, An-Ping Li, Zhigang Jiang, Edward H. Conrad, Claire Berger, Christoph Tegenkamp, Walt A. de Heer (2014): Exceptional ballistic transport in epitaxial graphene nanoribbons , Nature, 506, 349 (2014) weitere Informationen
DOI: 10.1038/nature12952