Graphene gates

A nanostructured quantum dot with tunable electronic properties can be carved from a single sheet of graphene with a reactive ion etching process

Credit: © 2008 AIP

The high carrier mobility and related characteristics of graphene — a monolayer sheet of carbon atoms packed in a two dimensional honeycomb lattice — are of interest from both a fundamental standpoint as well as for practical applications, such as nanoelectronic devices. In spite of the increasing wealth of knowledge about the physical properties of this material, however, there is a distinct lack of information about charge transport in graphene quantum dots.

The 'zero' bandgap of graphene has hindered experimental efforts to fabricate tunable quantum dots, and tunnelling phenomena inhibit the electrostatic confinement of carriers in these structures. Now, Christoph Stampfer and colleagues¹ at the ETH Zurich, Switzerland have fabricated a single-layer graphene quantum dot in which three lateral graphene gates are used to electrostatically control charge transfer between source and drain electrodes. The structure, comprising a 0.06 µm² graphene island connected to the source and drain electrodes through two 50-nm-wide constrictions, was produced by the reactive ion etching of a graphene sheet using an argon/oxygen gas mixture.

Low-temperature (1.7 K) transport measurements indicated the charging energy of the graphene dot to be ˜3.5 meV, which is consistent with its size. A further reduction in size of the graphene quantum dot in combination with measurements at even lower temperatures, may enable studies on carrier transport through individual quantum energy levels.