In 1991, while peering with an electron microscope at amorphic carbon - i.e.
soot - Japanese researcher Sumio Iijima observed strange, supremely long
threads a few atoms wide. These `threads' peeking out from among the soot turned
out to be hollow tubes formed by hexagonal carbon molecules; owing to their
extreme thinness and tubular shape scientists began to call them `nanotubes'.
A nanometre is a billionth of a metre, which is roughly the size of a nanotube's diameter. A row of about four
atoms can fit in a single nanotube.
In 2002, carbon nanotubes are more relevant than ever. Incredibly strong, stable
and electrically conductive, it has been predicted they will become the new
superstrong space-age material for cars and aeroplanes. The US National Aeronautics
& Space Administration NASA probably has the wildest vision: they have seriously
considered anchoring satellites that float at a height of 36,000 kilometres
to the ground with a rope made of carbon nanotubes. In theory, the project is
feasible. The tensile strength of carbon nanotubes is a hundredfold that of
steel, which according to calculations is more than enough to construct `a space
rope' or even a space lift.
Information technology revolution?
In the short run, it is the electronics industry that has the greatest expectations
for carbon nanotubes. Since the 1960s, the vertiginous development of the calculation
capacity of computers has been based on semiconductor technology, in which silicon
guides the electric impulses going through the computer's circuits. The smaller
the circuits can be made, the more efficiently and quickly the computer operates.
Owing to the physical characteristics of the element, however, silicon chips
cannot be made endlessly smaller. In today's computers, the silicon components
have been reduced to a size of some one hundred nanometres, but according to
theorists, it is enormously difficult to make them as small as twenty nanometres,
let alone smaller. With the current speed of development, we will reach a dead
end around the year 2010.
Nanotubes, however, are only about two nano-metres wide. According to some
estimates, nanotube electronics could be as much as a thousand times faster
than the current electronics based on silicon and metals. And to top it all,
the electric conductivity of nanotubes can be customised simply by choosing
a tube with a certain helicity. A straight tube behaves like metal, while a
twisted one acts as a semiconductor. Therefore, nanotubes could replace both
the semiconductors used in transistors, such as silicon, and the metal wires
that connect transistors, such as copper.
There are so far two basic problems in the way of the nanotube revolution.
Firstly, the manufacturing of nanotubes is very expensive: a gram of nanotubes
costs about a hundred US dollars. That is worth ten grams in gold! Secondly,
the construction of complex computer circuits requires new technologies so that
the electrical and mechanical characteristics of straight `basic' nanotubes
can be easily altered. It must also be possible to join nanotubes together to
form more complex constructions.
Simulation - a gate
to experimental research
Nanotechnology in general and carbon nanotubes in particular are becoming a
major business. Crossing the frontier of research, however, does not always
require huge early investments. The nanotube research group at the Accelerator
Laboratory, the University of Helsinki, is an excellent example of how it is
possible to participate in the nanoscientific avant-garde with meagre financial
"We use computer simulations to see what happens to nanotubes when they
are irradiated with ions or atomic clusters because ion irradiation is a good
tool to study and modify properties of nanotubes. In simulations, we can study
these dynamic processes in real time, which is not possible in experimental
conditions, as the processes in reality only last femtoseconds, which is a quadrillionth,
or million billionth, of a second," says Kai Nordlund, PhD, Academy
Fellow, who is in charge of the computational work in the nanotube group. The
nanotube group is part of the ion beam group of the Accelerator Laboratory which
is led by Professor Juhani Keinonen. Besides Nord-lund, the nanotube
group includes postdoctoral researcher Arkady Krasheninnikov and Emppu
Salonen, MSc, who has just completed his doctoral thesis.
Bombarding imaginary nanotubes with imaginary ions may sound like futile tinkering,
but quite the contrary. Through the simulations, it is possible to find solutions
such as how to `weld' single nanotubes together with ion beams to form the shape
of an X or an even more complex construction. These are the methods that the
electronic industry badly needs.
"At their best, the simulations can be used to predict new processes,
which means that we can also meet with surprises in the simulations. Of course,
that's the fun part of this work. A successful simulation can also lead to the
launch of experimental research. Who knows, in a couple of years our group may
well be experimenting with nanotubes," says Nordlund.
In fact, 70 per cent of the research conducted at the Accelerator Laboratory
is experimental. Nanotubes are bombarded virtually owing to the scarce availability
and minuscule size of the research material, but for the bombarding of larger
surfaces, formed by millions of atoms, the Laboratory has a real ion accelerator.
It has been used to target materials such as graphite, a close relative of nanotubes.
Nanotubes can be considered extremely narrow, single layers of graphite that
have been wrapped up into cylinders.
All tricks are known
Carbon is a thoroughly known element, which means that basically any physicist
with a powerful computer could start to simulate the impact of ion bombardment
on carbon nanotubes. The mathematical models used in the simulations were invented
well before the discovery of carbon nanotubes.
"It's true that almost any scientist could perform the same simulations.
But there are so many theoretical and practical problems connected with the
simulations that it can easily take a year to solve them. The competition is
so tough today that a year is too long," says Krasheninnikov, who has specialised
in nanotube modelling.
"In a way it's a question of capturing area. When you are a researcher
in some really hot field and want to stay in front, you must know what the other
trail blazers are doing right now," says Emppu Salonen, the postgraduate
of the group.
"Our speciality is a particular problem: the modelling of the ion irradiation
of nanotubes. When we started some eighteen months ago, we were the first in
the world. Our group is a lucky combination of know-how from different fields.
Arkady was familiar with nanotubes and quantum mechanical computation, while
we others have been working with irradiation for a decade and know all the tricks.
Even the models become unstable if you don't know what you're doing," says
Silicon sticks to its guns
Ultimately the nanotube revolution is a question of money. Even if scientists
succeeded in developing and modifying nanotubes, their production would become
the bottleneck. If NASA really wants to construct a 36,000-kilometre nanotube
rope for the price of a hundred dollars per gram, the final costs will be fairly
Today, there are about half a dozen companies producing nanotubes in the world.
Nordlund doubts, however, whether the price will ever be lowered enough. "Nanotubes
have great potential in electronics, but we should remember that since the 1960s
there have been promises about brand new materials that will beat silicon during
the next decade. Yet silicon has been sticking to its guns. I think that nanotubes
will find their own niche in the electronics industry, but I very much doubt
they will completely topple silicon chips.''
More moderate scientists have indeed been warning the business world of premature
triumph. So far only few commercial applications have succeeded with nanotubes.
The American car-manufacturing giant General Motors has mixed nanotubes in the
plastic parts of cars. During painting, an electric current is conducted into
the plastic mixed with nanotubes, which makes the paint stick harder to the
car's surface. On the other side of the globe, Korean Samsung has already begun
serial production of flat computer monitors where carbon nanotubes have been
used. The idea is that when a very weak electric current is conducted into the
nanotubes, they begin to transmit large quantities of electrons from their tips.
When hitting the surface of the phosphorised screen, the electrons activate
the phosphorus, and the monitor is lit.
There are also many who believe that nanotube compounds will soon replace carbon
fibre. Who knows, in the near future we might speed up with unbreakable nanotube
ski sticks and beat the tennis ball (or court) with an unbreakable tennis racket.
And maybe some day, after a century or two, take a nanotube lift into orbit.
What are nanotubes?
Nanotubes are a form of carbon, discovered in 1991. Other known forms of carbon
are fullerene, diamond, graphite and amorphic carbon, or soot.
Nanotubes consist of chains of pure carbon, the diameter of which is about
two nanometres, or two billionths of a metre. Their length can be several thousand
nanometres. If you think of an even, hexagonal sheet of graphite as chicken
wire mesh, the nanotube is like a rolled up piece of that mesh.
Owing to their molecular structure, nanotubes are extremely strong - they
endure bending better than the strongest carbon fibres and their tensile strength
is a hundredfold that of steel. The density of nanotubes, however, is only a
sixth of that of steel. Therefore, it is hoped nanotubes will provide new materials
for such as cars and aeroplanes.
By adjusting the size and structure of nanotubes, it is possible to make them
either conduct electricity like metals or act as silicon and other semiconductors,
that is, to conduct electricity only under the influence of an outside electromagnetic
or light pulse. Both metals and semiconductors are needed in advanced electronics.
The electrical conductivity of nanotubes has been estimated to be a billion
amperes per square centimetre. Copper wire burns and breaks, if an electrical
current of more than a million amperes passes a square centimetre thick wire.
Nanotubes remain stable in temperatures up to 3,000 degrees Centigrade, while
the metal wires in microchips melt in temperatures of 600 to 1,000 degrees centigrade.
Nanotubes are still extremely difficult to manufacture. Their current price
is about a hundred US dollars per gram.
What is materials physics based on ion beams?
In an ion beam, the material under study is irradiated with single, electrically
charged atoms, molecules or atomic clusters: ions. The ion beam is created with
an ion accelerator. Materials and applied physics based on ion beams have been
the main line of research at the Accelerator Laboratory of the University of
The ion beam method has been used for purposes such as developing extremely
thin diamond coatings that can be used to cover artificial joints; the diamond
coating protects the patient's body from metal compounds dissolving from the
Traditionally, ion beam based physics has been carried out by firing single
ions at large surfaces to enable the modification and study of the characteristics
of the irradiated area. Ion beams are also used in the characterisation of the
qualities of various materials.
The current trend in materials physics is to study and modify nanosize atomic
structures, that is, structures the size of a billionth of a metre, such as
The equipment at the Accelerator Laboratory is so far insufficient for bombarding
with ion beams objects the size of a few nanometres, such as single carbon nanotubes.
With the experience gained in ion irradiation of larger areas, however, the
nanotube research group of the Laboratory has developed powerful computer simulations
of the ion irradiation of nanotubes.
With the nanocluster accelerator, which will probably be taken into use at
the end of 2002, it is possible to irradiate nanosize clusters of ten to a million