Graphene, discovered in 2004 as a new phase of crystalline matter one atom thick,exhibits electronic conduction distinct from and superior to conventional metals andsemiconductors and thus opens new opportunities for device design and fabrication.
The single plane of graphite is now known to represent a new class of two-dimensional materials, one to several atoms in thickness that are conventionally crystalline in lateral dimensions micrometers to centimeters. The electrons in graphene move rapidlyin a way that resembles massless photons and nearly massless neutrinos. They indeed exhibit Klein tunneling, a quantum phenomenon of unit probability specular tunneling
through a high potential barrier that was originally conceived as a property of electrons and positrons in vacuum. These remarkable properties, endowed by the hexagonal “honeycomb” carbon-atom array onto ordinary electrons, fortunately are well explained by the methods of condensed matter physics, but that “explaining” has several initially puzzling aspects that we address.
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“Graphene” is the name given to a single-layer hexagonal lattice of carbon atoms,an extended two-dimensional lattice of benzene rings, devoid of hydrogen atoms. Thisone-atom-thick material has recently been found to be robust, if not completely planar,in samples tens of micrometers up to 30 inches in extent, on a supporting substrate.
Graphene is a contender in the new information technology (and other) applications,beyond being a scientific breakthrough and curiosity. As we will see, electrons in graphene display properties similar to photons and neutrinos, never before observed in a condensed-matter environment. The new electron properties arise in a straightforward way from the symmetry of the atomic positions and the resulting cone-shaped,rather than parabolic, regions in the electron energy surfaces. It is reassuring to see that all the new effects are well described by the Schr¨odinger-equation-based methods of condensed matter physics that have served well in understanding solids from semiconductors to superconductors. Dirac-equation-like electron behavior in graphene is obtained directly from appropriate simplification of the Schr¨odinger theory of atoms, molecules and solids. Beyond this, graphene is the first example of a new class of two-dimensional crystals, a new phase of matter. This is a surprise in many ways that offers new opportunities, especially, in electronics.
The discovery of graphene extends, beyond some theoretical predictions, what useful forms matter can take. It is truly a new paradigm.
The 2010 Nobel Prize in Physics was shared by Andre K. Geim and Konstantin S.Novoselov for their work on graphene. They had isolated and named the single layers in 2004. The method that they used, basically using Scotch tape to pull the graphite apart, was simple and accessible, and provided samples still the best available. This caused a rush of new experiments. Graphene, as they showed, was really only one example of a class of two-dimensional crystals that they had discovered. Their experimental work revealed the remarkable electronic properties of graphene, and they tied these to earlier work in relativistic particle physics. The material itself has unique and superior properties, both mechanically and electrically, and has many possible applications.
The explosion of publications related to graphene has been truly remarkable.A very recent review of the rapidly expanding literature and assessment of applications is given by Novoselov et al. (2012).
