Science

Tiny light mill could have big applications in nanotech

Tiny light mill could have big...
A gold light mill nanomotor embedded in a 300 nanometers-thick square-shaped silica microdisk (Image: Zhang group)
A gold light mill nanomotor embedded in a 300 nanometers-thick square-shaped silica microdisk (Image: Zhang group)
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The light mill's direction of rotation can be changed by altering the frequency of the laser light (Image: Zhang group)
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The light mill's direction of rotation can be changed by altering the frequency of the laser light (Image: Zhang group)
A gold light mill nanomotor embedded in a 300 nanometers-thick square-shaped silica microdisk (Image: Zhang group)
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A gold light mill nanomotor embedded in a 300 nanometers-thick square-shaped silica microdisk (Image: Zhang group)
The Berkeley Lab team, Ming Liu (foreground), Xiang Zhang and Thomas Zentgraf (Photo: Berkeley Lab Public Affairs)
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The Berkeley Lab team, Ming Liu (foreground), Xiang Zhang and Thomas Zentgraf (Photo: Berkeley Lab Public Affairs)
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OK, first of all, what’s a light mill? It’s a simple rotary motor consisting of four flat vanes mounted to a central axis, which spins when subjected to light. Light mills have been around since 1873, mostly just as novelty items, and have pretty much always been at least a few inches tall. Less than a week ago, however, scientists at California’s Lawrence Berkeley National Laboratory announced in a research paper that they had created a light mill just 100 nanometers in size. Unlike its bigger brothers, this tiny device might actually have some very practical applications.

The nano light mill rotates when exposed to laser light, and the speed and direction of the rotation can be changed by manipulating the frequency of that light. Most intriguingly, the mill can generate enough torque to drive a micrometer-sized silica disk, 4,000 times larger in volume than the mill itself. This means that the nano mill could conceivably be put to use, in things such as nanoelectromechanical systems (NEMS), nanoscale solar light harvesters, and nanobots that could perform actions such as unwinding and rewinding DNA double helixes.

The Berkeley Lab team, Ming Liu (foreground), Xiang Zhang and Thomas Zentgraf (Photo: Berkeley Lab Public Affairs)
The Berkeley Lab team, Ming Liu (foreground), Xiang Zhang and Thomas Zentgraf (Photo: Berkeley Lab Public Affairs)

The nano mill was constructed out of a gold-based metamaterial, which is the key to why it works. Metals contain plasmons, which are surface waves that roll through its conduction electrons. The amount of force exerted by light on a metallic nanostructure can be enhanced when the frequency of the light waves resonates with those plasmons. The metamaterial was designed to maximize this effect. Previous attempts at such motors had to be much larger in order to generate any torque, because they did not exploit the interaction between photons and plasmons.

While a single mill attached to a silica disk was indeed able to turn it, the Berkeley Lab researchers found that the torque could be greatly increased by attaching multiple mills. A disk with four mills, for instance, required just half the laser power to achieve the same rotational speed as a disk with only one. "By designing multiple motors to work at different resonance frequencies and in a single direction, we could acquire torque from the broad range of wavelengths available in sunlight," said lead author Ming Liu.

The research paper was published in the journal Nature Nanotechnology.

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8 comments
Liam Proven
I don't recognise this term "light mill", but what you're describing sounds to me like a radiometer. [Two names for the same thing. -Ed]
Breonte Brooks
i remember my 8th grade industrial tech teacher having a light mill...never imaged it would be made on the nanoscale... so, you they make nanosized electric generators???
T.A. Nasir
That would be the application. this could solve the problem of a power source for nano bots as mentioned in the article. there could be quite a few applications for this. Nano sized computers can work independently of an external power source for example and carry their own generation units on their persons.
BoilingOil
Interesting! The first thing I thought when starting to read this article, was: great replacement or enhancement for solar cells.
Yusuf Khan
All these new catalysts and nano-electronics are amazing but have one major problem, they are all expensive and come from gold and rare stuff.
Lorem Sum
am I the only one who notices this thing looks like a swastika? I mean I\'m not saying it isn\'t an awesome scientific breakthrough, I was just thinking you could throw in a light hearted joke about Nazis to acknowledge that it\'s the first thing most people think of when they look at this picture.
William H Lanteigne
There is a resemblance to a \"left-handed\" swastika, as used by various cultures previous to the Nazi \"right-handed\" swastika.
There are no \"light-hearted\" jokes about Nazis.
anewton
Proven fan designs have 5 blades, not 4. These kids today Sheesh! :-)