Drawing conclusions from graphene
The unique electronic properties of graphene – a one-atom-thick sheet of carbon that was produced for the first time just two years ago – make it an ideal testing ground for fundamental physics, describe Antonio Castro Neto, Francisco Guinea and Nuno Miguel Peres
In a time when cutting-edge scientificresearch is expensive and complex, it seems absurd that a breakthrough in physics could be achieved with simple adhesive tape. But in 2004, Andre Geim, Kostya Novoselov and co-workers at the University of Manchester in the UK did just that. By delicately cleaving a sample of graphite with sticky tape, they produced something that was long considered impossible: a sheet of crystalline carbon justone atom thick, known as graphene. Many physicists believed that a 2D crystal like graphene would always roll up rather than stand free in a planar form; but Geim’s group brought to an end years of unsuccessful attempts to isolate graphene, and was able to visualize the new crystal using a simple optical microscope (figure 1). The single-layered honeycomb structure of graphene makes it the “mother”of all carbon-based systems: the graphite we find in our pencils is simply a stack of graphene layers; carbon nanotubes are made of rolledup sheets of graphene; and buckminsterfullerene molecules, or “buckyballs”, are nanometre-size spheres of wrapped-up graphene (figure 2). These forms of
Physics World November 2006
carbon were isolated long before graphene and have been used in manyapplications, but their electric, magnetic and elastic properties all originate in the properties of graphene. Just months after the initial discovery, Geim’s group improved its method for producing graphene. Rather than ripping sheets of carbon from graphite with adhesive tape, the team produced higher-quality graphene by gently pushing small graphite crystals along a hard surface – using a techniqueakin to drawing with a pencil. Soon after, a group headed by Philip Kim at Columbia University in the US confirmed the existence of graphene using the same drawing technique, while Walt de Heer and Claire Berger at Georgia Tech developed an epitaxial growth process that may be suitable for mass-producing graphene for industrial applications. Despite only being isolated two years ago, graphene hasalready appeared in hundreds of papers. The reason is that the material has unique properties arising from its honeycomb-lattice structure that could allow us to observe strange relativistic effects at speeds much slower than the speed of light. In addition, our ability
Antonio Castro Neto is at Boston University in the US, e-mail firstname.lastname@example.org; Francisco Guinea is at ICMM-CSIC in Spain; and NunoMiguel Peres is at Minho University in Portugal
Feature: Graphene 1 A sticky success
Graphene was first isolated by Andre Geim’s team at the University of Manchester just two years ago using the surprisingly simple technique of ripping layers from a graphite surface using adhesive tape. By repeatedly peeling away thinner layers (left), single-atom-thick sheets wereobtained (right), as shown in these scanning electron micrographs.
to manipulate the motion of the electrons in graphene studied extensively in the 1960s, and the remarkable paves the way to virtually lossless and ultrafast transis- agreement between the theoretical predictions of properties such as the heat capacity and the experimental tors with atomic dimensions. data is regarded as one of thegreatest successes of condensed-matter physics. Massless electrons We are already familiar with massless Dirac fermiGraphene’s unique properties arise from the collective behaviour of electrons. That in itself is nothing new: ons in high-energy particle physics: neutrinos. But as summarized in Philip Anderson’s famous dictum neutrinos have no electric charge and therefore do not “more is...