Graphene - one layer of carbon atoms arranged in a hexagonal lattice - is the
newest member in the family of carbon allotropes. Although isolated graphene was
reported for the first time only in 20041, the
progress it made over these years is enormous, and it rightly has been dubbed
"the wonder material".
There are three major areas of excitement about graphene. Firstly, it is the
first example of two-dimensional atomic crystal, which very existence improves
our understanding about thermodynamic stability of low-dimensional systems.
Secondly, the electronic properties of graphene are very peculiar: electrons in
graphene obey linear dispersion relation (just like photons), thus mimicking
massless relativistic particles2. And the last but
not least, many properties of graphene are superior to those in all other
materials, so it is very tempting to use it in a variety of applications,
ranging from electronics to composite materials.
Historically, it is the electronic properties which attracted most of
attention. Electrons in graphene behave like massless relativistic particles,
which governs most of its electronic properties. Probably one of the most
spectacular consequences of such unusual dispersion relation is the observation
of half-integer Quantum Hall Effect and the absence of localisation2. The later might be very important for graphene-based
field effect transistors.
Generally crystals of graphene could be prepared with very few defects
(consequence of ultra strong carbon-carbon bonds), which, in conjunction with
the absence of localisation and high Fermi velocity ensures very high mobility
of the charge carriers and short time of flight in ballistic regime. First
prototypes of high-frequency transistors have been recently developed and
demonstrated very encouraging characteristics3.
Also peculiar are graphene's optical properties. It has been measured that
graphene absorbs 2.3% of light4 - quite a sizable
fraction for an ultimately thin material. What is even more exciting is the fact
that this number is given solely by the combination of fundamental
constants4: πα (π=e2/hc≈1/137 is the fine
structure constant). Do it at home, multiply 3.14… by 1/137 and you will get
something close to 0.023.
Such combination of high conductivity (sheet resistance of doped graphene can
be as low as 10 Ohm) and low light adsorption makes this material an ideal
candidate for transparent conductive coating. Graphene utilisation for this type
of applications has been recently demonstrated by constructing graphene-based
liquid crystal5 and solar cells6.
Furthermore, the general issue of graphene mass-production (until recently
only research-size graphene samples have been available) has been resolved for
these sort of applications with the introduction of a novel technique: large
area thin films of micrometer-size graphene flakes can be produced by chemical
exfoliation of graphite5.
It is very tempting to use the unique properties of graphene for
applications. The already mentioned examples do not even nearly exhaust the list
of technologies which would benefit from using graphene. Composite materials and
photodetectors, support for bio-objects in TEM and mode-lockers for ultrafast
lasers - all those and many more areas would gain strongly from using graphene.
The issue, however, was always the mass-production of this material. Since
the very first experiments1, the technique of choice
for graphene production for many researchers was the very naïve "Scotch-tape
method"1,2 - simple peeling of
graphene monolayers from bulk graphite with an adhesive tape. However, recent
months seen a dramatic progress in development of truly mass-production
techniques for graphene synthesis. Ranging from aforementioned chemical
exfoliation to epitaxial growth (for a review see7),
these techniques give us a realistic hope that soon we will see products based
on this exciting two-dimensional material.
1. Novoselov, K. S., Geim, A. K., Morozov, S. V., Jiang, D.,
Zhang, Y., Dubonos, S. V., Grigorieva, I. V. & Firsov, A. A. "Electric Field
Effect in Atomically Thin Carbon Films" Science 306, 666-669 (2004).
2. Geim, A. K. & Novoselov, K. S. "The Rise of Graphene" Nature
Mater. 6, 183-191 (2007).
3. Yu-Ming Lin, Keith A. Jenkins,
Alberto Valdes-Garcia, Joshua P. Small, Damon B. Farmer & Phaedon Avouris,
"Operation of Graphene Transistors at Gigahertz Frequencies" Nano Lett., 9 (1),
4. R. R. Nair, P. Blake, A. N. Grigorenko,
K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres, & A. K. Geim "Fine
Structure Constant Defines Visual Transparency of Graphene" Science 320, 1308
5. Peter Blake, Paul D. Brimicombe, Rahul R. Nair, Tim
J. Booth, Da Jiang, Fred Schedin, Leonid A. Ponomarenko, Sergey V. Morozov,
Helen F. Gleeson, Ernie W. Hill, Andre K. Geim, & Kostya S. Novoselov
"Graphene-Based Liquid Crystal Device" Nano Letters 8(6) 1704 - 1708
6. X. Wang, L. Zhi, & K. Mullen, "Transparent,
conductive graphene electrodes for dye-sensitized solar cells" Nano Letters
8(1), 323-327 (2008)
7. A. K. Geim "Graphene: Status and
Prospects" Science 324, 1530-1534 (2009).
Copyright AZoNano.com, Dr. Kostya Novoselov (University of