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Nanotubes weigh the atom
www.physorg.com/news165504348.html
June 29th, 2009
(PhysOrg.com) -- How can you weigh a single atom? European researchers
have built an exquisite new device that can do just that. It may
ultimately allow scientists to study the progress of chemical
reactions, molecule by molecule.
Carbon nanotubes are ultra-thin fibres of carbon and a nanotechnologist’s dream.
They are made from thin sheets of carbon only one atom thick - known
as graphene - rolled into a tube only a few nanometres across. Even
the thickest is more than a thousand times thinner than a human hair.
Interest in carbon nanotubes blossomed in the 1990s when they were
found to possess impressive characteristics that make them very
attractive raw materials for nanotechnology of all kinds.
“They have unique properties,” explains Professor Pertti Hakonen of
Helsinki University of Technology. “They are about 1000 times stronger
than steel and very good thermal conductors and good electrical
conductors.”
Hakonen is coordinator of the EU-funded CARDEQ project which is
exploiting these intriguing materials to build a device sensitive
enough to measure the masses of atoms and molecules.
Vibrating strings
A carbon nanotube is essentially an extremely thin, but stiff, piece
of string and, like other strings, it can vibrate. As all guitar
players know, heavy strings vibrate more slowly than lighter strings,
so if a suspended carbon nanotube is allowed to vibrate at its natural
frequency, that frequency will fall if atoms or molecules become
attached to it.
It sounds simple and the idea is not new. What is new is the delicate
sensing system needed to detect the vibration and measure its
frequency. Some nanotubes turn out to be semiconductors, depending on
how the graphene sheet is wound, and it is these that offer the
solution that CARDEQ has developed.
Members of the consortium have taken the approach of building a
semiconducting nanotube into a transistor so that the vibration
modulates the current passing through it. “The suspended nanotube is,
at the same time, the vibrating element and the readout element of the
transistor,” Hakonen explains.
“The idea was to run three different detector plans in parallel and
then select the best one,” he says. “Now we are down to two. So we
have the single electron transfer concept, which is more sensitive,
and the field effect transistor concept, which is faster.”
Single atoms
Last November, CARDEQ partners in Barcelona reported that they had
sensed the mass of single chromium atoms deposited on a nanotube. But
Hakonen says that even smaller atoms, of argon, can now be detected,
though the device is not yet stable enough for such sensitivity to be
routine. “When the device is operating well, we can see a single argon
atom on short time scales. But then if you measure too long the noise
becomes large.”
CARDEQ is not alone in employing carbon nanotubes as mass sensors.
Similar work is going on at two centres in California - Berkeley and
Caltech - though each has adopted a different method to measuring the
mass.
All three groups have announced they can perform mass detection on the
atomic level using nanotubes, but CARDEQ researchers provided the most
convincing data with a clear shift in the resonance frequency.
But a single atom is nowhere near the limit of what is possible.
Hakonen is confident they can push the technology to detect the mass
of a single nucleon - a proton or neutron.
“It’s a big difference,” he admits, “but typically the improvements in
these devices are jump-like. It’s not like developing some well-known
device where we have only small improvements from time to time. This
is really front-line work and breakthroughs do occur occasionally.”
Biological molecules
If the resolution can be pared down to a single nucleon, then
researchers can look forward to accurately weighing different types of
molecules and atoms in real time.
It may then become possible to observe the radioactive decay of a
single nucleus and to study other types of quantum mechanical
phenomena.
But the real excitement would be in tracking chemical and biological
reactions involving individual atoms and molecules reacting right
there on the vibrating nanotube. That could have applications in
molecular biology, allowing scientists to study the basic processes of
life in unprecedented detail. Such practical applications are probably
ten years away, Hakonen estimates.
“It will depend very much on how the technology for processing carbon
nanotubes develops. I cannot predict what will happen, but I think
chemical reactions in various systems, such as proteins and so on,
will be the main applications in the future.”
The CARDEQ project received funding from the FET-Open strand of the
EU’s Sixth Framework Programme for ICT research.
More information: www.cardeq.eu/
Provided by ICT Results
www.physorg.com/news165504348.html
June 29th, 2009
(PhysOrg.com) -- How can you weigh a single atom? European researchers
have built an exquisite new device that can do just that. It may
ultimately allow scientists to study the progress of chemical
reactions, molecule by molecule.
Carbon nanotubes are ultra-thin fibres of carbon and a nanotechnologist’s dream.
They are made from thin sheets of carbon only one atom thick - known
as graphene - rolled into a tube only a few nanometres across. Even
the thickest is more than a thousand times thinner than a human hair.
Interest in carbon nanotubes blossomed in the 1990s when they were
found to possess impressive characteristics that make them very
attractive raw materials for nanotechnology of all kinds.
“They have unique properties,” explains Professor Pertti Hakonen of
Helsinki University of Technology. “They are about 1000 times stronger
than steel and very good thermal conductors and good electrical
conductors.”
Hakonen is coordinator of the EU-funded CARDEQ project which is
exploiting these intriguing materials to build a device sensitive
enough to measure the masses of atoms and molecules.
Vibrating strings
A carbon nanotube is essentially an extremely thin, but stiff, piece
of string and, like other strings, it can vibrate. As all guitar
players know, heavy strings vibrate more slowly than lighter strings,
so if a suspended carbon nanotube is allowed to vibrate at its natural
frequency, that frequency will fall if atoms or molecules become
attached to it.
It sounds simple and the idea is not new. What is new is the delicate
sensing system needed to detect the vibration and measure its
frequency. Some nanotubes turn out to be semiconductors, depending on
how the graphene sheet is wound, and it is these that offer the
solution that CARDEQ has developed.
Members of the consortium have taken the approach of building a
semiconducting nanotube into a transistor so that the vibration
modulates the current passing through it. “The suspended nanotube is,
at the same time, the vibrating element and the readout element of the
transistor,” Hakonen explains.
“The idea was to run three different detector plans in parallel and
then select the best one,” he says. “Now we are down to two. So we
have the single electron transfer concept, which is more sensitive,
and the field effect transistor concept, which is faster.”
Single atoms
Last November, CARDEQ partners in Barcelona reported that they had
sensed the mass of single chromium atoms deposited on a nanotube. But
Hakonen says that even smaller atoms, of argon, can now be detected,
though the device is not yet stable enough for such sensitivity to be
routine. “When the device is operating well, we can see a single argon
atom on short time scales. But then if you measure too long the noise
becomes large.”
CARDEQ is not alone in employing carbon nanotubes as mass sensors.
Similar work is going on at two centres in California - Berkeley and
Caltech - though each has adopted a different method to measuring the
mass.
All three groups have announced they can perform mass detection on the
atomic level using nanotubes, but CARDEQ researchers provided the most
convincing data with a clear shift in the resonance frequency.
But a single atom is nowhere near the limit of what is possible.
Hakonen is confident they can push the technology to detect the mass
of a single nucleon - a proton or neutron.
“It’s a big difference,” he admits, “but typically the improvements in
these devices are jump-like. It’s not like developing some well-known
device where we have only small improvements from time to time. This
is really front-line work and breakthroughs do occur occasionally.”
Biological molecules
If the resolution can be pared down to a single nucleon, then
researchers can look forward to accurately weighing different types of
molecules and atoms in real time.
It may then become possible to observe the radioactive decay of a
single nucleus and to study other types of quantum mechanical
phenomena.
But the real excitement would be in tracking chemical and biological
reactions involving individual atoms and molecules reacting right
there on the vibrating nanotube. That could have applications in
molecular biology, allowing scientists to study the basic processes of
life in unprecedented detail. Such practical applications are probably
ten years away, Hakonen estimates.
“It will depend very much on how the technology for processing carbon
nanotubes develops. I cannot predict what will happen, but I think
chemical reactions in various systems, such as proteins and so on,
will be the main applications in the future.”
The CARDEQ project received funding from the FET-Open strand of the
EU’s Sixth Framework Programme for ICT research.
More information: www.cardeq.eu/
Provided by ICT Results
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