Micrometer-sized drones (Microdrons with light-driven nanomotors) print only with light and precise control: this is the first time that physicists at the University of Würzburg have succeeded. Their microdrones are much smaller than red blood cells.
The hand-held laser pointer has no noticeable retracting forces when fired – even if it emits a direct stream of light particles. The reason is the very high weight compared to the very small recoil caused by light particles when leaving the laser pointer. However, it has long been clear that optical reflection forces can have a very large effect on the same small particles. For example, comet tails move from the Sun with light pressure. The operation of light spacecraft using light sails has been discussed several times, most recently in connection with (Microdrons with light-driven nanomotors) the “hooting star” project, in which a fleet of small spacecraft is sent to Alpha Centauri.
Common quadcopter drones as models
In the journal Nature Nanotechnology, the physicists of Würzburg, led by Professor Bert Hecht (chairman of Experimental Physics 5, Nano-Optics Group), have now shown for the first time that not only micrometer-sized objects can be efficiently propelled into the aquatic environment. light, but also it controls almost all three levels of freedom (two translational plus one rotational).
In addition, they were inspired by conventional quadcopter drones, in which four independent rotors allow full control of movements. Such control capabilities offer entirely new possibilities for the often extremely difficult handling of nano- and micromaterials, for example for the assembly of nanostructures, for surface analysis, with nanometer precision or in the field of reproductive medicine.
Polymer disks with up to four light-driven nanomotors
Würzburg microdrons consist of a transparent polymer disk with a diameter of 2.5 micrometers. Up to four independently addressable nanomotors made of gold are built into this disk.
“These motors are based on optical antennas developed in Würzburg, that is, on small metal structures with dimensions smaller than the wavelength of light,” said Xiaofei Wu, the group’s postdoc. in Hecht research. “These antennas are specially optimized to receive circularly polarized light. This allows the motors to receive light regardless of the orientation of the drone, which is important for use. In the next step, the received light energy is then released by the motor in a specific direction to create an optical return force that depends on the direction of polarization rotation (clockwise or counterclockwise) and in one of two different wavelengths of light. ”
Only with this idea can researchers control their microdrons efficiently and accurately. Due to the very light weight of the drones, extreme speeds can be achieved.
The development of microdrones is challenging. It started in 2016 with a research grant from the VW Foundation dedicated to risky projects (press release, University of Würzburg, German)
Safe production based on single crystal gold
Precise design of nanomotors is essential for the operation of microdrones. The use of accelerated helium ions as a means of cutting nanostructured nanostructured gold has changed the game. In the next steps, the drone body was made by electron lithography. Finally, the drones must be removed from the substrate and transferred to the solution.
In further experiments, a feedback loop was introduced that automatically corrected out-of-microdron effects and controlled them more accurately. In addition, the research team is working to complete control options so that the length of drones above the surface can be controlled. And, of course, another goal is to incorporate tools that can be used on microdrones.
