Plastics unite to make unexpected 'metal'
- From: as <assidd73@xxxxxxxxx>
- Date: Sun, 6 Jul 2008 00:15:49 -0700 (PDT)
Full article:
http://technology. newscientist. com/article/ dn14140-plastics -unite-
to- make-un
expected-metal. html
Plastics unite to make unexpected 'metal'
Jamming the right two pieces of plastic together creates a thin but
strongly
conducting channel along the junction that acts like a metal, say
Dutch
researchers. The discovery could lead to a whole new way of making
electronics from non-metallic materials, and even new superconductors.
Alberto Morpurgo's <http://med.tn. tudelft.nl/ people/web. php?23>
team at
Delft University of Technology in the Netherlands attached a
micrometer-thick crystal of the organic polymer TTF
<http://en.wikipedia .org/wiki/ Tetrathiafulvale ne> to a similarly
thin
organic crystal of the polymer TCNQ.
The thin, flexible crystals conform to each other's shape and stick
together
due to van der Waals <http://en.wikipedia .org/wiki/ Van_der_Waals_
force>
forces, says Morpurgo.
Metal surprise
Both TTF and TCNQ are electrical insulators. But Morpurgo's team found
that
a 2-nanometre- thick strip along the interface between the two
crystals
conducts electricity as well as a metal.
It was known that a blend of the two materials could conduct
electricity,
but it does so relatively poorly.
When laid side-by-side the two materials are physically unchanged, but
the
way electrons behave is subtly altered along the interface where the
different materials are in close proximity, says Morpurgo. In tests,
they
tried cooling down the combined materials, expecting the odd behaviour
to
disappear because the two plastics become more insulating at lower
temperatures.
Instead the interface became a better conductor, just as metals offer
less
resistance to electricity when they are cooled.
Usually the electrons inside each of the materials are unable to
travel
freely. But Morpurgo thinks that at the interface electrons from the
TTF
molecules are able to jump over to vacant spaces known as "holes" in
the
TCNQ molecules.
Interesting properties
The result is that, in the 2-nm gap between the molecules of the two
different materials, they can travel freely, allowing current to flow.
"Such
an electron-hole system is really something new and it may have
interesting
electronic properties," Morpurgo says.
Jochen <http://www.physik. uni-augsburg. de/exp6/group/ mannhart_
e.shtml>
Mannhart at the University of Augsburg in Germany agrees. "You do get
exciting things happening at interfaces - physics at interfaces is
responsible for the behaviour of semiconductors, for instance."
But the TTF-TCNQ interface conducts electricity much better than
standard
semiconductors. "The electron concentration there is an order of
magnitude
higher," Mannhart says. "That has the power to create new effects,
from
magnetism to superconductivity. "
Journal reference:
<http://technology. newscientist. com/article/ 10.1038/nmat2205>
Nature
Materials (DOI: 10.1038/nmat2205)
.
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