Tiny Motor Powered by Single Molecule

A molecule-sized motor that can spin clockwise and counterclockwise could one day power tiny machines. CREDIT: CEMES-CNRS and Univ. P. Sabatier (Toulouse) View full size image

Engineers dream of motors made out of single molecules that could jump-start the production of machines on the molecular level. However, simply modeling them after larger motors has been extremely difficult.

Now, researchers from France and the University of Ohio have collaborated on a new approach and created the first compact molecular motor that can spin both clockwise and counterclockwise.

“What must be done [to create a working molecular motor] is to start from the bottom, to forget about the macroscopic scale,” said Christian Joachim, one of the lead authors of this project from the Centre d’Elaboration Materiaux et d’Etudes Structurales in Toulouse, France.

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The molecule is 1 nanometer high and 2 nanometers across, and is called a "piano-stool complex" because of its shape. It has a nonmoving three-legged base standing on a gold surface and a rotating top, or rotor, with a single atom of ruthenium connecting the two. This rotor contains five iron spokes, one of them shorter than the others to easily detect when it spins.

The motor operates using a quantum mechanical process called inelastic electron tunneling, in which electrons that are shot at the molecule lose some of their energy in the transfer and the resulting vibrations turn the rotor.

The researchers transferred the motor molecules onto the gold, and their rotors started spinning on their own, even at minus 316 degrees Fahrenheit. A scanning tunneling microscope hovered above the motor, testing its capabilities by stimulating different regions of the molecule.

The researchers found they could control the rotation of the motor by focusing energy onto different parts of the tiny motor. For example, targeting each of the longer spokes creates counterclockwise movement, while targeting the shorter one creates clockwise movement.

“[The motor] is a ‘concept-molecule’ whose goal is to improve our knowledge about the rotation driving of a single molecule,” Joachim said.

The researchers are now focusing on two goals: hooking the motor to a chain of nanometer-size gears and working to install it into a molecular nano-car in order to power and drive it.

This study was published online on Dec. 23 in the journal Nature Nanotechnology.

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