The Rice Of Grafhene

THE RISE OF GRAPHENE
A.K. Geim and K.S. Novoselov
Manchester Centre for Mesoscience and Nanotechnology,
University of Manchester, Oxford Road M13 9PL, United Kingdom
Graphene is a rapidly rising star on the horizon of materials science and condensed matter physics. This
strictly two-dimensional material exhibits exceptionally high crystal and electronic quality and, despite its
shorthistory, has already revealed a cornucopia of new physics and potential applications, which are
briefly discussed here. Whereas one can be certain of the realness of applications only when commercial
products appear, graphene no longer requires any further proof of its importance in terms of
fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a
newparadigm of “relativistic” condensed matter physics, where quantum relativistic phenomena, some of
which are unobservable in high energy physics, can now be mimicked and tested in table-top experiments.
More generally, graphene represents a conceptually new class of materials that are only one atom thick
and, on this basis, offers new inroads into low-dimensional physics that has never ceased tosurprise and
continues to provide a fertile ground for applications.
Graphene is the name given to a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D)
honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities (Figure 1). It
can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite.Theoretically,
graphene (or “2D graphite”) has been studied for sixty years1-3 and widely used for describing properties of
various carbon-based materials. Forty years later, it was realized that graphene also provides an excellent
condensed-matter analogue of (2+1)-dimensional quantum electrodynamics4-6, which propelled graphene into a
thriving theoretical toy model. On the other hand, although known asintegral part of 3D materials, graphene was
presumed not to exist in the free state, being described as an “academic” material5 and believed to be unstable
with respect to the formation of curved structures such as soot, fullerenes and nanotubes. All of a sudden, the
vintage model turned into reality, when free-standing graphene was unexpectedly found three years ago7,8 and,
especially, whenthe follow-up experiments9,10 confirmed that its charge carriers were indeed massless Dirac
fermions. So, the graphene “gold rush” has begun.

MATERIALS THAT SHOULD NOT EXIST
More than 70 years ago, Landau and Peierls argued that strictly two-dimensional (2D) crystals were
thermodynamically unstable and could not exist11,12. Their theory pointed out that a divergent contribution of
thermalfluctuations in low-dimensional crystal lattices should lead to such displacements of atoms that they
become comparable to interatomic distances at any finite temperature13. The argument was later extended by
Mermin14 and is strongly supported by a whole omnibus of experimental observations. Indeed, the melting
temperature of thin films rapidly decreases with decreasing thickness, and they becomeunstable (segregate into
islands or decompose) at a thickness of, typically, dozens of atomic layers15,16. For this reason, atomic
monolayers have so far been known only as an integral part of larger 3D structures, usually grown epitaxially on
top of monocrystals with matching crystal lattices15,16. Without such a 3D base, 2D materials were presumed not
to exist until 2004, when the commonwisdom was flaunted by the experimental discovery of graphene7 and
other free-standing 2D atomic crystals (for example, single-layer boron nitride and half-layer BSCCO)8. These
crystals could be obtained on top of non-crystalline substrates8-10, in liquid suspension7,17 and as suspended
membranes18.
Importantly, the 2D crystals were found not only to be continuous but to exhibit high crystal...