At 1nm across, this is the smallest electric motor, or so claims Tufts University in Massachusetts.
The ‘motor’ sits on a copper surface and is a butyl methyl sulphide molecule with a sulphur atom at the centre and carbon atoms radiating off to form two arms with four carbons on one side and one on the other.
“The excitement is in the demonstration that you can provide electricity to a single molecule and get it to do something that’s not just random,” said lead researcher Dr Charles Sykes.
Spinning single-molecules are not new.
“Until now they’ve been driven by either chemicals or light,” said Tufts, pointing out that only electrical power can be aimed at a single molecule: “Even very tightly focused light will hit many molecules at once”.
With the scanning tunnelling microscope, “we can land just on top of one molecule, measure it and spin it,” said Sykes.
The motor is a dc machine and its mechanism is not electromagnetic nor electrostatic in the usual sense, but more mechanical.
“It is much more akin to a biological system,” Sykes told Electronics Weekly. “Electrons excite quite energetic vibrations in the backbone of the molecule, and these decay into stretches and eventually lower energy rotations. The trick is that it the molecule is asymmetric and acts like a ratchet and pawl.”
On the copper surface, the 1nm molecule is centred just to one side of a single (0.25nm diameter) copper atom.
The experiment had to be done cold – 5K was chosen where the molecule spins at 50rev/s.
“That’s because as temperatures rise, the motor spins much faster, far beyond the ability of the scientists to measure the rotations,” said Tufts. “At 100K, a molecular motor spins more than a million times per second.”
“It’s not that we couldn’t work at a higher temperature,” added Sykes. “It’s just that too much is happening. At that speed, it’s just a blur.”
And the future?
“We will try and learn all we can about how these molecular motors work,” said Sykes, adding that he and his colleagues “will also study how the energy can be transferred to other molecules and make arrays of tiny cogs or gears on surfaces.”
Resting on a copper (orange) surface, the yellow ball is the molecule’s sulphur base, and the two arms are composed of carbon and hydrogen atoms. Current comes through the tip of a scanning tunnelling microscope, and can direct the molecule in one direction or another, said Tufts University.
The work is published in Nature Nanotechnology this week.
Is it really a motor?
This is an amazing piece of chemical engineering, but is the result really a motor?
Probably not, until current is delivered through a nano-structure attached to the same substrate, is the view of Electronics Weekly.
Email email@example.com with ‘motor’ in the subject box if you have a different opinion.