Microscopic metavehicles powered by nothing but light

Date:
September 28, 2021
Source:
Chalmers University of Technology
Summary:
Researchers have succeeded in creating tiny vehicles powered
by nothing but light. By layering an optical metasurface onto a
microscopic particle, and then using a light source to control it,
they succeeded in moving the tiny vehicles in a variety of complex
and precise ways -- and even using them to transport other objects.



FULL STORY ========================================================================== Researchers from Chalmers University of Technology, Sweden, have succeeded
in creating tiny vehicles powered by nothing but light. By layering an
optical metasurface onto a microscopic particle, and then using a light
source to control it, they succeeded in moving the tiny vehicles in a
variety of complex and precise ways -- and even using them to transport
other objects.


========================================================================== Light has an inherent power to move microscopic objects -- a property previously used to develop the Nobel prize winning research idea of
'optical tweezers', which use a highly focused laser beam to control
and manoeuvre tiny particles with incredible precision.

Now, a research group at Chalmers University of Technology and the
University of Gothenburg has shown how even an unfocused light can be
used to manoeuvre microscopic particles in a controlled manner. Their
research was recently published in the journal Nature Nanotechnology.

The researchers manufactured vehicles at a scale of 10 micrometres
wide and 1 micrometre thick -- one thousandth of a millimetre. The
vehicles consisted of a tiny particle, coated with something known as a 'metasurface'. Metasurfaces are ultra-thin arrangements of carefully
designed and ordered nanoparticles, tailored to direct light in
interesting and unusual ways. They offer fascinating possibilities for
use in advanced components for optical applications such as cameras, microscopes and electronic displays. Usually, they tend to be thought
of as stationary objects, with their use being seen as the ability to
control and affect light. But here, the researchers looked at it the
other way around, investigating how the forces resulting from the light's change in momentum could be used to control the meta-surface.

Like two pool balls colliding The researchers took their microscopic
vehicles, which they termed 'metavehicles', and placed them on the
bottom of a water dish, then used a loosely focused laser to direct
a plane wave of light onto them. By a purely mechanical process --
the heat generated by the light plays no part in the effect -- the
vehicles could then be moved in a variety of patterns. By adjusting the intensity and polarisation of the light, the researchers succeeding
in controlling the vehicles' movement and speed with a high level of
precision, navigating them in different directions and complex patterns,
such as figures of eight.



========================================================================== "According to Newton's third law, for every action there is an equal and opposite reaction -- this means that when the light hits the meta-surface,
and is deflected in a new direction, the meta-surface is also pushed away
in the other direction. Imagine playing pool, when two balls hit each
other and bounce off in different directions. In this case, the photons
and the meta surface are like those two pool balls," explains Mikael
Ka"ll, Professor at the Department of Physics at Chalmers University of Technology, co-author of the article and leader of the research project.

Transporting other small objects "The metavehicles were stable,
and their navigation was highly predictable and controllable. With
advanced automated feedback systems, and more sophisticated control of
the intensity and polarisation of the source light, even more complex navigation would be possible," explains Daniel Andre'n, formerly of the Department of Physics at Chalmers and lead author of the study.

The researchers also experimented with using the metavehicles as
transporters, to push small particles around the tank. The metavehicles
proved capable of transporting objects including a microscopic polystyrene
bead and a yeast particle through the water with ease. They even succeeded
in pushing a dust particle 15 times the size of the metavehicle itself.

At the moment, the practical applications of this discovery may be a
way off.

But the fundamental nature of the research means that its value may not
yet be evident.

"In the exploration of optical forces, there are many interesting effects
that are not yet fully understood. It is not applications that drive this
type of research, but exploration of the different possibilities. In a
number of different stages ahead, you never know what will happen. But
the fact that we showed how the metavehicles can be used as transporters
is the most initially promising potential application, for example to
move particles through cell solutions," explains Mikael Ka"ll.

Video of the metavehicles in action:
https://www.youtube.com/ watch?v=CMkRSquPWk0 ========================================================================== Story Source: Materials provided by
Chalmers_University_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Daniel Andre'n, Denis G. Baranov, Steven Jones, Giovanni Volpe,
Ruggero
Verre, Mikael Ka"ll. Microscopic metavehicles powered and steered
by embedded optical metasurfaces. Nature Nanotechnology, 2021; 16
(9): 970 DOI: 10.1038/s41565-021-00941-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210928075021.htm

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