[tt] [nano] nanodot: heated SCNT-in-a-SCNT can act as transporter, in one direction

Thu Apr 17 10:56:32 UTC 2008

(
abstract:
http://www.sciencemag.org/cgi/content/abstract/1155559v1
,
http://nanotechweb.org/cws/article/tech/33753
and
http://technology.newscientist.com/article/dn13643-nanoscale-freighter-hauls-its-first-load.html
)

Reports

Submitted on January 22, 2008
Accepted on March 31, 2008

Subnanometer Motion of Cargoes Driven by Thermal Gradients along Carbon
Nanotubes
Amelia Barreiro 1, Riccardo Rurali 2, Eduardo R. Hern«¡ndez 3*, Joel
Moser 1, Thomas Pichler 4, Laszlo Forro 5, Adrian Bachtold 1*

1 CIN2 Barcelona and CNM-CSIC, Campus UAB, E-08193 Bellaterra, Spain.
2 Departament d¡ÇEnginyeria Electr«Ònica, UAB, 08193 Bellaterra, Spain.
3 Institut de Ci«²ncia de Materials de Barcelona, Campus UAB, E-08193
Bellaterra, Spain.
4 Faculty of Physics, University of Vienna, Strudlhofgasse 4, 01090
Wien, Austria.
5 EPFL, CH-1015 Lausanne, Switzerland.

* To whom correspondence should be addressed.
Eduardo R. Hern«¡ndez , E-mail: ehe at icmab.es
Adrian Bachtold , E-mail: adrian.bachtold at cnm.es

An important issue in nanoelectromechanical systems is developing small
electrically driven motors. We report on an artificial nanofabricated
motor in which one short carbon nanotube moves relative to another
coaxial nanotube. A cargo is attached to an ablated outer wall of a
multiwall carbon nanotube that can rotate and/or translate along the
inner nanotube. The motion is actuated by imposing a thermal gradient
along the nanotube, which allows for sub-nanometer displacements, as
opposed to an electromigration or random walk effect.

---

Apr 11, 2008
Nanotube 'monorail' moves cargo

Researchers in Europe have built a "monorail" from carbon nanotubes that
can transport a fleck of metal over a distance of about 800 nm. The
metal cargo sits on a 5-nm long nanotube "sleeve" surrounding a much
longer nanotube "rail" that is stretched across a trench in a silicon
chip. Surprisingly, the team believes the sleeve is driven by lattice
vibrations called phonons  rather than electrical interactions, which
they originally thought would propel the device.
Nanotube 'monorail'
Nanotube 'monorail'

Carbon nanotubes are sheets of carbon one atom thick that are rolled up
into tubes that are only several nanometres in diameter. Adrian Bachtold
and colleagues at the Autonomous University of Barcelona along with
collaborators at the University of Vienna and the Swiss Federal
Institute of Technology in Lausanne built their device using a
multiwalled nanotube, which comprises several concentric nanotubes.
www.nanotechweb.org/cws/lp/cws75

The team began by attaching a 1500-nm long multiwalled tube across the
trench with metal electrodes. They then used an electrical-breakdown
technique to remove several outer layers from most of the nanotube,
leaving a short sleeve that could rotate freely and move to and fro
along the inner rail.
Hotter in the middle

The team operate the motor by passing an electrical current through the
rail, which causes it to heat up. However, the region of the rail in the
middle of the trench becomes much hotter than the ends  because the
electrodes act as heat sinks. If the sleeve and its cargo  a tiny piece
of gold  are placed in the middle of the trench, they will move to one
side of the trench at speeds of up to 1 m/s.

 This is a beautiful experimental resultRamin Golestanian, University of
Sheffield 

Bachtold told physicsworld.com that the team had originally hoped that
they could apply a voltage between the electrodes to encourage atomic
interactions between the rail and sleeve, causing the sleeve to move in
a helical manner in one direction  and then in the other direction when
they reversed the voltage. Such motion was expected, according to
Bachtold, because the atoms on the inner and outer nanotubes would both
be arranged in slightly different spiral configurations.

Instead, the team found that the sleeve always moved away from the
centre of the trench. According to Bachtold, the first clue that heat
was driving the motion was that the gold cargo particle changed shape by
partially melting. The team confirmed the role of heating by doing
computer simulations of the system.
Phonon propulsion

Heat is transported through carbon nanotubes in the form of quantized
lattice vibrations called phonons, which behave much like particles.
Copious numbers of phonons are created at the hot centre of the rail and
move towards both electrodes, striking the outer sleeve and dragging it
along with them.

Ramin Golestanian of the University of Sheffield describes the work as
"a beautiful experimental result". However Golestanian, who studies the
physics of moving nanoparticles and nanomechanical devices, told
physicsworld.com that much more investigation is required to understand
the mechanism responsible for the motion and the role of phonons in it.

Bachtold and colleagues have now turned their attention to making more
practical motors based on the effect. They are currently working on
reversible devices in which one end of the rail is heated and the other
is not, which should cause the sleeve to move from the hot end to the
cold end. The direction of travel could be reversed by simply switching
which end is heated.

In the longer term, Bactold believes that such motors could be used to
drive nanometre-sized machines, such as those that perform drug delivery
or other medical functions in the body.

The researchers presented their work in Science.
About the author

Hamish Johnston is editor of physicsworld.com

----

Nanoscale freighter hauls its first load

 * 19:00 10 April 2008
 * NewScientist.com news service
 * David Robson

A nanoscale "monorail" that can creep along a nanotube track has shifted
its first load, hauling a gold nugget a distance of 0.5 micrometres. The
device could be a useful addition to microscopic construction toolkits
that researchers hope will advance computing and other fields.

The new device developed by researchers in Spain, Austria and
Switzerland is made from two nanotubes nested like the parts of a
telescope.

The central tube is one micrometer long and acts as a rail for the
second, smaller, 200-nanometre nanotube. The outer "monorail carriage"
is driven by applying current to the inner rail, and can move in both
directions along the rail  it can also rotate around it.

In trials, the device was used to transport a ball of gold about 250
nanometres wide along the track for a distance of 500 nanometres (0.5
micrometres). It moves at speeds ranging from 0.1 nanometres per second
to 1 micrometre per second. The researchers observed the motion using an
atomic force microscope.
Range of movement

"It is the first nano-freighter train," says Andrea Ferrari, an expert
in nano-engineering from the University of Cambridge, UK, who was not
involved in the research.

Previous nanomotors could only rotate around one axis. The monorail's
greater range of movement provides another mechanism for scientists
searching for ways to work with nanoscale components as they would with
larger objects in a conventional workshop.

The monorail is driven by the heat energy from the electric current
flowing through the nanotube, says Adrian Bachtold from the Institut
Catal«¢ de Nanotecnologia in Barcelona, Spain, who worked on the device.
When the current is applied a temperature gradient forms, leaving the
middle of the rail nanotube at more than 1000 ¢ëC, with either end at
just 27 ¢ëC.
Minimal friction

Computer simulations showed that vibrations travel from the hot to the
cold areas, carrying the monorail with them. At the moment, the monorail
nanotube can only move towards the ends of the rail nanotube from the
centre, but the team are working on giving it a reverse gear.

The device was made by zapping carbon-rich material with electricity to
grow an initial pair of nested nanotubes. The team ran a large electric
current through, making the outer layer come free from the one nested
inside. They then burned off most of its length to create the shorter,
free-moving monorail carriage.

"The beautiful thing about this device is that the friction between the
two nanotubes is very small  the surfaces are almost atomically
smooth," says Bachtold.

Ferrari was impressed by the work, saying it advanced previous
demonstrations of nanotransport. "However, this is just a first step and
significant research and development work is needed to make this a real
technology."

Journal reference: Science (DOI: 10.1126/science.1155559)

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