CHEMICAL & ENGINEERING
ffiWSluieiiffi OCTOBER 2Λ. 2005 - EDITED BY W I L L I A M G. SCHULZ & MELISSA KUHNELL
NANOTECHNOLOGY
NANOCAR ROLLS INTO ACTION World's first molecular car zips about on fullerene wheels
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UTOMAKERS ARENT LOSING
any sleep over a car recently unveiled by Rice University researchers. Forget about rich Co rinthian leather. This new coupe doesn't have any seating or steer ing. On the upside, though, with a wheelbase less than 5 nm, parking it is unlikely to be a problem. The new auto is the world's first single-molecule car. A group led by chemistry professorJames 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 engi neering professor Kevin F. Kelly and his lab, the team drove this nanocar around on a gold surface by using the tip of a scanning tun neling 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, accord ing to Tour. "It's the beginning of learning how to manipulate things at the nanolevel in nonbiological systems," he says. Once scientists figure out how to control an object's movements on the nanoscale, Tour explains, they can develop means of mo lecular transport and construc tion that could ultimately lead to a controlled assembly system akin to the way enzymes work in bio logical systems. The nanocar took eight years for Tour's lab to complete. When they began the project, they were WWW.CEN-ON
LINE.ORG
ing parked until the surface was heated above 170 °C—presum ably because of strong adhesion between the fullerene wheels and the underlying gold. Between 170 °C and 225 °C, the nanocars moved around by translational motion and pivot ing, the researchers observed. The translational motion was always in a direction perpendicular to the nanocar's axles, indicating that the nanocar 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
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 transitionmetal catalysts, and the axles and chassis are syn thesized via pal ladium-catalyzed coupling reac tions. Attaching the wheels had to be the last step of the synthesis, but getting four fullerenes onto the molecule in sufficiently high yield was n o t trivial. The group al so ran into other roadblocks with solubility and imaging and had to go back to the drawing board to redesign the nanocar several times. Tour says ON A ROLL World's first single-molecule car (model shown) can they call the cur- move and pivot on a gold surface. rent version of the nanocar the "Z-series" because pulling it forward. Tour explains it sort of looks like the letter Z. that the STM tip's electric field might polarize the molecule so To show that the nanocars ac the tip can tow the nanocar us tually roll around on their fuller ing electrostatics. Tour says the ene wheels, rather than slipping group has subsequently built a and sliding like a car on ice, the nanotruck that can transport Rice team introduced the nano molecular cargo as well as a lightcars onto a flat gold surface. They driven motorized nanocar.—BETH found the nanocars were quite ANY HALFORD stable on the surface—remain C&EN
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