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“World’s smallest car” built
Oct. 22, 2005
Courtesy Rice University
and World Science Staff
Humvee, move over.
Scientists say they have made the world’s smallest car—a single-molecule “nanocar” that
has wheels, axles and a chassis. They describe the device in a paper due to appear in an upcoming issue of the
research journal
Nano Letters.
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A model of the nanocar. (Y. Shira/Rice University)
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An image showing the inferred motion of the
nanocar (T. Sasaki/Rice University)
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Building
such machines is a step toward regularly manufacturing things of this size,
which could be useful for many purposes, said
James M. Tour of Rice University in Houston, Texas, one of the developers.
“We’d eventually like to move objects and do work in a controlled fashion on the molecular scale, and these vehicles are great test beds for that. They’re helping us learn the ground rules.”
The nanocar has a pivoting suspension and freely rotating axles, the
researchers said. The wheels are buckyballs, spheres of pure carbon containing 60 atoms apiece.
“Nanoscale” objects
like this reported car are objects whose sizes are measured in nanometers, or millionths of a millimeter.
The car is just 3 or 4 nanometers wide, making it slightly wider than a strand of
DNA, the researchers said. A human hair, by comparison, is about 80,000 nanometers
wide.
Other research groups have created nanoscale objects that are shaped like
automobiles. But study co-author Kevin F. Kelly, also of Rice, claimed Rice’s vehicle is the first that actually functions like a car, rolling on four wheels in a direction perpendicular to its axles.
Kelly and his group provided measurements and experimental evidence that they said verified the rolling movement, using a super-powerful microscope known as scanning tunneling microscope.
“It’s fairly easy to build nanoscale objects that slide around on a surface,” Kelly said. “Proving that we were rolling – not slipping and sliding – was one of the most difficult parts of this project.”
To do that, Kelly and graduate student Andrew Osgood measured the movement of the nanocars across a gold surface. At room temperature, strong electrical bonds hold the wheels tightly against the gold, but heating frees them to roll.
To show that the cars were rolling rather than sliding, Kelly and Osgood took scanning tunneling microscope images every minute and watched the cars progress. Because nanocars’ axles are slightly longer than the wheelbase – the distance between axles –
they said they could determine the way the cars were oriented and whether they moved perpendicular to the axles.
In addition, the team said they found a way to grab the cars and pull them. Tests showed it was easier to drag the cars in the direction of wheel rotation than
sideways.
Tour’s research group said they spent almost eight years perfecting the techniques to make
the nanocars. Much of the delay involved finding a way to attach the wheels without destroying the rest of the
car, the researchers explained.
The team said they have already followed up the nanocar work by designing a
light-powered nanocar and a nanotruck capable of carrying a payload.
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