Geology Reference
In-Depth Information
Box 9.6 Novel forms of carbon
In 2004, russian-born physicists andré Geim and Kostya
Novoselov published the remarkable discovery that
single
layers
can be peeled from a crystal of graphite simply by
repeated application of sticky tape! the resulting graphite
monolayers - just one atom thick and so dubbed '2D
crystals' - have been found to have astonishing nanotech-
nological properties, so distinct from ordinary graphite as
to merit a new chemical name -
graphene
. as well as open-
ing an entirely new field of physics, graphene (Figure 9.6.1a)
promises a host of novel technological applications, from
ultrafast electronic devices to highly efficient photovoltaic
collectors (Geim and Kim, 2008).
But graphene is just the most recently discovered of a
number of new structural forms of carbon that have come
to light in the laboratory - and (in some cases) in nature
too - since 1985. that was when British chemist harry
Kroto and teams from rice (texas) and Sussex (UK)
universities discovered C
60
molecules with a distinctive
spherical geometry that assembled themselves spont-
aneously from hot ionized carbon vapour. these mole-
cules were made up of alternating 5- and 6-membered
rings reminiscent of a soccer ball. the rings have delo-
calized
π
-electrons similar to graphene, and indeed the
molecule can be thought of as a spherical derivative of
graphene (Figure 9.6.1b). Owing to its geometric similarity
to the iconic 'Geodesic Dome' designed for the US
exhibit at expo 67 in Montreal by architect Buckminster
Fuller, the C
60
molecule was named
buckminsterfullerene
(Figure 9.6.1b),
3
although the shorter name 'buckyballs'
is more commonly used today! Infrared spectra show that
C
60
and C
70
exist in young planetary nebulae in interstellar
space, but they are also found in ordinary terrestrial soot.
Other members of the fullerene structural family take
hollow cylindrical form with diameters in the nanometre
range, visualized as 'rolled up' versions of a graphene
sheet (Figure 9.6.1c). Such
carbon nanotubes
4
(which may
be single- or multiwalled) can be engineered to have a
huge variety of properties of value in nanotechnology.
Carbon nanotubes are the strongest and stiffest materials
yet discovered.
the
π
-electrons in graphene make it too conducting for
some potential applications. It can be transformed into
insulating sheets by attaching one hydrogen atom to each
carbon atom in the sheet, forming a new class of com-
pounds, devoid of
π
orbitals, called
graphanes
.
3
One of a family of similar molecules (including C
70
) called
fullerenes.
4
Known in the russian literature since the 1950s, but redis-
covered more recently in the West.
(a)
(b)
(c)
(d)
Figure 9.6.1
(a) a single sheet of graphene, showing how its basic sheet structure relates to (b) buckminsterfullerene
(C
60
'buckyballs'), (c) carbon nanotubes, and (d) graphite. (Source: Geim and Lovoselov (2007). reprinted by permission
of Macmillan publishers Ltd).
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