Microdrones with light-driven nanomotors

Date:
April 21, 2022
Source:
University of Wu"rzburg
Summary:
Physicists have managed to propel micrometer-sized drones precisely
using light only. Their microdrones are significantly smaller than
red blood cells.



FULL STORY ========================================================================== Propelling micrometre-sized drones using light only and exerting precise control: Physicists at the University of Wu"rzburg have succeeded at
this for the first time. Their microdrones are significantly smaller
than red blood cells.


==========================================================================
A hand-held laser pointer produces no noticeable recoil forces when it is "fired" -- even though it emits a directed stream of light particles. The reason for this is its very large mass compared to the very small recoil impulses that the light particles cause when leaving the laser pointer.

However, it has long been clear that optical recoil forces can indeed have
a very large effect on correspondingly small particles. For example, the
tails of comets point away from the Sun partly due to light pressure. The propulsion of light spacecrafts via light sails has also been discussed repeatedly, most recently in connection with the "star shot" project,
in which a fleet of miniature spacecrafts is to be sent to Alpha Centauri.

Ordinary quadcopter drones as models In the journal Nature Nanotechnology, Wu"rzburg physicists led by Professor Bert Hecht (Chair of Experimental
Physics 5, Nano-Optics Group) have now shown for the first time that
it is possible to not only efficiently propel micrometre-sized objects
in an aqueous environment with light, but also control them precisely
on a surface with all three degrees of freedom (two translational plus
one rotational).

In doing so, they were inspired by ordinary quadcopter drones, where
four independent rotors allow complete control of the movements. Such
control possibilities offer completely new options for the usually
extremely difficult handling of nano- and micro-objects, for example,
for the assembly of nanostructures, for the analysis of surfaces with
nanometre precision, or in the field of reproductive medicine.



========================================================================== Polymer discs with up to four light-driven nanomotors The Wu"rzburg
microdrones consist of a transparent polymer disc measuring 2.5
micrometres in diameter. Up to four independently addressable nanomotors
made of gold are embedded in this disc.

"These motors are based on optical antennas developed in Wu"rzburg, --
that is, tiny metallic structures with dimensions less than the wavelength
of light," says Xiaofei Wu, a postdoc in the Hecht research group. "These antennas were specifically optimised for receiving circularly polarised
light. This allows the motors to receive the light regardless of the orientation of the drone, which is crucial for applicability. In a
further step, the received light energy is then emitted by the motor in
a specific direction to generate optical recoil force, which depends on
the sense of rotation of the polarisation (clockwise or counterclockwise)
and on either of two different wavelengths of light." It was only with
this idea that the researchers were able to control their microdrones efficiently and precisely. Due to the very small mass of the drones,
extreme accelerations can be achieved.

The development of the microdrones was challenging. It started back
in 2016 with a research grant by the VW Foundation dedicated to risky
projects.

Precise fabrication based on single-crystal gold The extremely precise fabrication of the nanomotors is crucial for the function of the
microdrones. The use of accelerated Helium ions as a means to cut nanostructures from monocrystalline gold has turned out to be a game
changer.

In further steps, the drone body is produced using electron beam
lithography.

Finally, the drones must be detached from the substrate and brought
into solution.

In further experiments, a feedback loop is being implemented to
automatically correct external influences on the microdrones to control
them more precisely.

Furthermore, the research team strives to complete the control
options so that the height of the drones above the surface can also be controlled. And of course, another goal is to attach functional tools
to the microdrones.


========================================================================== Story Source: Materials provided by University_of_Wu"rzburg. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xiaofei Wu, Raphael Ehehalt, Gary Razinskas, Thorsten Feichtner,
Jin Qin,
Bert Hecht. Light-driven microdrones. Nature Nanotechnology, 2022;
DOI: 10.1038/s41565-022-01099-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421130941.htm

--- up 7 weeks, 3 days, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)