Graphene, the chicken wire sheets of carbon, akin to an unrolled single-walled carbon nanotube, one might say, could be the next big thing in molecular electronics. Andre Geim and Kostya Novoselov from The School of Physics and Astronomy at The University of Manchester recently showed that graphene can be carved into tiny electronic circuits with individual transistors having a size not much larger than that of a molecule.
Now, US researchers have performed the first scanning tunnelling spectroscopy studies of graphene flakes equipped with a gate electrode. Their findings could help explain graphene’s unique behaviour as well as leading the way to new ways to build components from this material.
Melissa Panlasigui, Michael Crommie, Yuanbo Zhang, and Victor Brar. (Credit: Roy Kaltschmidt, Lawrence Berkeley National Laboratory)
Michael Crommie and colleagues at the Lawrence Berkeley National Laboratory and the University of California at Berkeley have revealed some surprises into the electronic behaviour of the two-dimensional crystal form of carbon, known as graphene. Graphene resembles a thin honeycomb, or chicken wire fencing in which a single carbon exists at the vertices of tessellated hexagons.
Known features investigated previously include novel nanometre-scale behaviour such as electronic scattering, spin-based phenomena, and collective excitations. It is also predicted to be sensitive to charge-carrier density. One particular feature revealed by the team is an unexpected gap in the energy spectrum of electrons tunnelling into graphene’s single layer of atoms. This peculiar feature arises because of the interaction of the tunnelling electrons with the vibrations of the 2D graphene crystal, the quantised phonons.
STM spectra of the graphene surface at different gate voltages reveal electronic behaviour of the device. (Credit: Lawrence Berkeley National Laboratory)
Monolayer graphene, comprised of flakes just one carbon atom thick, were first isolated by Andrew Geim’s group at The University of Manchester, England, in 2005, and have been intensely studied since then. Graphene’s interesting electronic effects opens a new realm of basic science, says Crommie, It’s an entirely new material, with new physics that could lead to new practical devices and applications. In that respect it’s as promising as carbon nanotubes – but graphene’s planar geometry is potentially even more versatile.
Crommie adds that Because graphene is two-dimensional, it can be carved up and cut into tailored shapes, like cutting a sheet of paper. The shape might include features like narrow sections to control the flow of electrons, edges with unique magnetic properties, and dopant atoms implanted at precise locations in the 2D matrix.
Zhang, Y., Brar, V.W., Wang, F., Girit, C., Yayon, Y., Panlasigui, M., Zettl, A., Crommie, M.F. (2008). Giant phonon-induced conductance in scanning tunnelling spectroscopy of gate-tenable graphene. Nature Physics DOI: 10.1038/nphys1022
Further reading
Nature Phys., 2008, in press
http://dx.doi.org/10.1038/nphys1022
Crommie Group Homepage
http://www.physics.berkeley.edu/research/crommie/index.html
Mesoscopic Physics Group, The University of Manchester
http://onnes.ph.man.ac.uk/nano/index.html