"The molecular barrow is the first step to understanding the basic mechanical movements of a 'simple' molecule on a surface," Hao Tang of CEMES told nanotechweb.org. "After the experimental validation of this system, we will focus on building more complex molecular machines."
The barrow consists of a central board, two rear legs and two front wheels. It is driven along a copper surface by manipulating the rear legs with the tip apex of a scanning tunnelling microscope (STM). The STM also measures the rotation of the front wheels by tracking the changes in tunnel current intensity between the tip apex and the surface through the barrow board, axle and wheels.
The team designed a molecule with a tetracene unit as the board of the barrow, tert-butyl phenyl groups for the rear legs and triptycene molecules for the front wheels. The scientists successfully synthesized the wheel-axle-wheel component of this barrow, thus proving that the molecule is feasible.
However, through a series of simulations, the researchers found that friction effects meant that, to make the front wheels move, they needed to incorporate two ratchet molecular groups on the central board.
According to Tang, the ratchets play two major roles. "The first one is to constrain the wheels to rotate in one direction," he said. "Secondly the ratchets help to keep the wheels in contact with the surface more strongly. In this way the friction is increased and the rotation is facilitated." The scientists have yet to synthesize this second design of barrow.
"The next step is to synthesize the molecular barrow, deposit the molecule on a copper (211) surface, do manipulations in our ultra-high-vacuum, low-temperature STM and record the rotation signals," added Tang.
While Tang says that the device does not have any commercial applications in the near future, he reckons that in the long term the understanding of molecular machines could be used to conceive intelligent materials or drugs.