Counting on nano control: Molecular machines

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  • Published: Jan 15, 2013
  • Author: David Bradley
  • Channels: Atomic
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In a spin over nano

STM microscopy and attendant I-V spectroscopy at the atomic scale has allowed an international team to take the next step in creating nanoscale machines. Their work now reveals a multi-component molecular motor that can be moved clockwise and anticlockwise. Credit: Saw-Wai Hla)

STM microscopy and attendant I-V spectroscopy at the atomic scale has allowed an international team to take the next step in creating nanoscale machines. Their work now reveals a multi-component molecular motor that can be moved clockwise and anticlockwise.

Researchers from France, Singapore and the USA have collaborated on taking nanoscale machinery to the next level of control allowing them to control whether or not a rotor rotates clockwise or anticlockwise functionality that has not previously been achieved.

Saw-Wai Hla of Ohio University and colleagues worked with Christian Joachim of A*Star in Singapore and CEMES/CNRS in France and Gwenael Rapenne of CEMES/CNRS. Control is essential to the success of nano machines given that they operate on the boundary between the quantum world and the macroscopic world. Writing in Nature Nanotechnology, the researchers explain how they have used the electrons generated by a scanning tunnelling microscope (STM) to control the rotation of a motor just 2 nanometres long and half that distance high as it sits on a gold crystal surface.

Greater bearing on nano motor

The upper part of the motor consisting of five arms, four of which contain iron and the fifth without making it shorter,  is attached to the surface by a single ruthenium atom, which acts like a "ball bearing", and is attached via sulfur groups.

At a chilly 80 Kelvin, the motor remains agitated by thermal energy but at just above 5 Kelvin, the team found that it stops rotating. At this much cooler temperature, they were then able to control its rotation using applied electron energy to different parts of the motor to make it rotate clockwise or anticlockwise.

The directional rotation arises from sawtooth-like rotational potentials, which are solely deter- mined by the internal molecular structure and are independent of the surface adsorption site, as revealed by the current-voltage (I-V) spectroscopic studies, the team explains. "In addition to the I-V spectroscopy to measure the energy required to rotate the motor, we also used current vs. time (I-t) spectroscopy at a fixed bias to rotate the molecule and also to measure the rotational rate," Hla told SpectroscopyNOW.

"If we want to build an actual device based on this motor, we would install electrodes on the surface to create an energy source," Hla explains. The team is now making plans for more sophisticated and controllable nanomachines in work funded by the AUTOMOL project, the US Department of Energy, the A*STAR Atom Tech VIP programme phase III, CNRS and the University Paul Sabatier of Toulouse.

"Asymmetries in the rotation energy potential and inelastic tunnelling effects lead to unidirectional motion in both clockwise and anticlockwise directions by selectively exciting different subunits of the motor. This finding will further accelerate the development of complex and automated nanomachinery that can be operated on a material surface," the team reports. Hla told us that, "For the next step, we are extending the work using more complex molecular machines. One thing we want to explore is to find the limit of quantum machines by looking at molecular machines having different sizes."

Related Links

Nature Nanotechnol, 2013, 8, 46-51: "Controlled clockwise and anticlockwise rotational switching of a molecular motor"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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