Graphene conducts electron waves in discrete units
Experimental physicists from the University of Groningen have for the first time observed the wave properties of electrons as they move through a narrow strip of graphene. They altered the wavelength of the electrons in a graphene transistor. The electrical conductivity was found to change discretely as a function of the wavelength. With this work, the researchers have made an important step towards the discovery of new quantum mechanical effects in graphene transistors. They published their results yesterday online in the renowned journal Nature Physics.
Graphene, a one-atom-thick layer of carbon atoms, is a highly promising material in nanotechnology. It was first isolated from bulk graphite in 2004 by Andre Geim and Konstantin Novoselov, who received the Nobel Prize for Physics for this in 2010. Graphene is a superb thermal and electrical conductor with unusual electronic properties. An electron can behave classically as a sort of billiard ball that can freely move in a strip of graphene and rebound at the edges. An electron can also be described quantum mechanically as a wave with a specific wavelength. The theory predicts that reducing the width of a graphene structure to just a few nanometres can result in new quantum mechanical effects, such as the changing of metallic graphene into a semiconducting material
Zigzag edge
Up until now, it had been expected that these effects would only occur in graphene structures with edges that are perfect at an atomic scale. From a technical viewpoint, it is not yet possible to manufacture perfect edges. Scientists from the Zernike Institute for AdvancedMaterials in Groningen have now experimentally shown that such quantum mechanical effects are even possible for a zigzag edge. They have demonstrated that the number of electron waves that fit in the graphene strip determines its electrical conductivity
Experimental feat
For these effects to be observed, it is vital that the graphene transistor contains as few impurities as possible. As most impurities are found in the substrate, the choice was made in this experiment to detach the graphene layer from the substrate by selectively removing the polymer substrate under the graphene transistor. This led to a suspended graphene transistor of the highest possible electronic quality. A following step is to investigate if these effects can also be observed in a graphene transistor that is manufactured on a substrate with as few impurities as possible, for example on a boron nitride crystal
Reference
Quantized conductance of a suspended graphene nanoconstriction , N.Tombros et al.
More information
Niko Tombros, telephone +31 (0)50 363 89 74 and Bart van Wees, telephone +31 (0)50 363 49 33