Issue Date: October 24, 2005
Nanocar Rolls Into Action
Automakers arent losing any sleep over a car recently unveiled by Rice University researchers. Forget about rich Corinthian leather. This new coupe doesnt have any seating or steering. On the upside, though, with a wheelbase less than 5 nm, parking it is unlikely to be a problem.
The new auto is the worlds first single-molecule car. A group led by chemistry professor James M. Tour constructed the tiny four-wheeler from an oligo(phenylene ethynylene) chassis and axle covalently mounted to four fullerene wheels. With the help of electrical engineering professor Kevin F. Kelly and his lab, the team drove this nanocar around on a gold surface using the tip of a scanning tunneling microscope (STM) (Nano Lett., published online Oct. 13, dx.doi.org/10.1021/nl051915k).
Building a working nanocar represents the first step toward molecular manufacturing, according to Tour. Its the beginning of learning how to manipulate things at the nanolevel in nonbiological systems, he says.
The nanocar took eight years for Tours lab to complete. When they began the project, they were able to assemble the chassis and axles in just six months. Adding the fullerene wheels proved far more difficult. The problem, Tour says, is that fullerenes shut down reactions mediated by transition-metal catalysts, and the axle and chassis are synthesized via palladium-catalyzed coupling reactions. Attaching the wheels had to be the last step of the synthesis, but getting four fullerenes onto the molecule in sufficiently high yield was not trivial.
To show that the nanocars actually roll around on their fullerene wheels, rather than slipping and sliding like a car on ice, the Rice team introduced the nanocars onto a flat gold surface. They found the nanocars were quite stable on the surface—remaining parked until the surface was heated above 170 C—presumably because of strong adhesion between the fullerene wheels and the underlying gold.
Between 170 C and 225 C, the researchers observed that the nanocars moved around by translational motion and pivoting. The translational motion was always in a direction perpendicular to the nanocars axle, indicating that it moves by rolling rather than sliding.
The Rice group also was able to directly control the movement of an individual car by placing an STM tip in front of the car and pulling it forward. Tour explains that the STM tips electric field might polarize the molecule so the tip can tow the nanocar using electrostatics. Tour says the group has subsequently built a nanotruck that can transport molecular cargo as well as a light-driven motorized nanocar.
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