Teraflop 73 - Novembre - cesca

The discoveries of fullerenes
and nanotubes, both of which
took place in close succession
in the mid 1980s and early
1990s, have marked the start of scientific
revolution in the fields of physics,
chemistry and materials science, and
have greatly contributed to bringing
nanotechnology to the attention of scientists,
technocrats and even the general
public. Few in the scientific community
had dared to imagine that so
extensively-studied an element as
carbon could still hide secrets of this
calibre. Furthermore, soon after these
discoveries it was realised that these
fascinating novel materials had many
interesting properties, not always present
in other more conventional forms
of carbon, and these properties conferred
to them an immense scope for
technological applications. Today,
there is probably not a single university
web page in the world where you
cannot find a picture of a fullerene or
nanotube lurking somewhere, and
this in itself testifies to the interest
these nanostructures have generated.
Fullerenes are closed cage-like
structures which contain hexagonal
rings of carbon, as found in graphite,
but in order for these structures to be
closed, they must also contain exactly
twelve pentagons, which curve the
structure so that it folds and closes on
itself. C 60, the most famous of the
fullerenes, looks exactly like a football,
only it has a diameter of less than
1 nm (10 -9 metres). Each of the twelve
pentagons is surrounded by five
hexagons, and there are twenty hexagons
in total. The fullerenes were discovered
by chance in 1985, when a
team of British and American scientists
were trying hard to synthesise
chains of carbon atoms, which they
thought could exist in space, and
Fullerenes, Nanotubes and Related
Nanostructures:
A Paradigm of Nanotechnology
Eduardo Hernández
Institut de Ciència de Materials de Barcelona
CSIC
The structure of the Buckminsterfullerene
isomer of C60. could be responsible for certain unaccounted-for
spectral lines in the radiation
received in Earth. When
analysing the product of their synthesis
experiments in a mass spectrometer
they found that many carbon clusters
of different sizes were obtained,
but for clusters with sizes larger than
20-30, amazingly, all clusters had an
even number of carbon atoms, and
the cluster of size 60 seemed to be
specially stable. By appropriately tuning
the conditions of their experiments
they were able to obtain essentially
C 60 alone, which again confirms
the special stability of this cluster
size. It was when trying to understand
why this size was so favoured, that
these scientists came up with the proposal
of the C 60 structure known as
Buckminsterfullerene, in honour of
Buckminster Fuller, the famous American
architect and mathematician. The
Buckminsterfullerene structure of C 60
was confirmed some years later, by a
German research team, which was
able to synthesise C 60 in sufficient
quantities as to form fullerite, a molecular
solid of C 60 clusters, and identify
the structure using crystallographic
techniques. In 1996 Prof. Harry Kroto,
from Sussex University in England,
and Profs. Richard Smalley and
Robert Curl, from Rice University in
the United States, were awarded the
Nobel Prize in Chemistry for the role
they played in the discovery of C 60
and the fullerenes.
Fullerenes immediately attracted
a great deal of attention to themselves,
and many scientific teams around the
world started performing experiments
or conducting theoretical studies to
better understand and characterise
these novel structures. And it was in
this way that fullerenes lead to the subsequent
discovery (or re-discovery, in
fact) of carbon nanotubes. These were
found in the carbon soot that resulted
from a fullerene synthesis experiment,
when this was observed in a transmission
electron microscope by the
Japanese scientist Sumio Iijima, although
it appears that nanotubes had
previously been observed as early as
in 1975 by another Japanese scientist
working in France, Morinobu Endo.
Nanotubes are tubular structures,
made of seamlessly rolled-up graphite
layers (graphene). They come in two
types: multi-wall nanotubes, consisting
of several graphene layers, which can
be several nanometers in diameter, or
single-wall, with a diameter typically
between 1 and 2 nm (though smaller
and larger diameters have also been
observed). In either case their length
is much larger than their diameter, so
they are essentially one-dimensional
structures. Nanotubes were yet another
surprise that carbon kept hidden
(or at least not fully disclosed), although
now it is known that nanotubes
can be made of other materials forming
layered structures similar to
graphite, such as BN, WS 2,MoS2, Bi,
etc. However, it is still the case that carbon
nanotubes, especially single-wall