[AI] Graphite - not graphene - could replace silicon transistors;
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Tue Jan 29 11:48:21 EST 2008
Graphite - not graphene - could replace silicon transistors;
Single-atom-thick layers of carbon have been touted as
an alternative to the silicon transistor, but now it
looks as if their multi-layered cousin might be a
A REPLACEMENT for the silicon transistor - the heart of the modern
computer - may be closer than expected, thanks to a material
discovered in the 16th century.
For the last 20 years, the number of transistors that can be
fitted onto a computer chip has doubled about every two years.
This trend can't continue indefinitely, however, as shrinking
silicon transistors down eventually makes them less efficient.
Recently a substance called graphene - hexagonal arrays of carbon
atoms in sheets one atom thick - has been touted as . One hundred
times thinner than the smallest silicon transistor possible,
graphene conducts electricity much more efficiently. It also has
exotic electronic properties which could be useful in quantum
But there's a problem: graphene sheets tend to curl up and react
with substances around them, making them difficult to build into
devices. Now Yakov Kopelevich and Pablo Esquinazi of the State
University of Campinas in Brazil claim that graphite, the
substance used in pencil leads, might be a more useful
alternative to silicon (Advanced Materials , DOI:
10.1002/adma.200702051). "All the properties of graphene are
present in grahite," says Kopelevich. He and Esquinazi point out
that graphite, which is made of multiple stacks of graphene
sheets, is easier and cheaper to produce and doesn't curl up,
thanks to the stabilising effect of the adjacent layers.
In the last few years the pair have shown that, as with graphene,
graphite's conductivity can be altered using a magnetic field and
that current can flow through it as though carried by massless
"particles" called Dirac fermions. Both properties will be
important in future quantum computers.
"It's good that we don't have to think only one layer [of carbon
atoms] will do everything," says Jorge Sofo, a graphene
researcher at Pennsylvania State University.
But according to Millie Dresselhaus, a nano-electronics expert at
the Massachusetts Institute of Technology, how much of the magic
of graphene is found in graphite remains to be seen. It is not
clear if graphite's electronic properties can be tuned to suit a
specific application, for example, something done easily in
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