Researchers made vehicles at a scale of 10 micrometers wide and 1 micrometer thick – one thousandth of a millimeter. The vehicles were made of a tiny particle, covered with an element known as the “metasurface”. Metasurfaces are ultra-thin arrays of carefully designed and ordered nanoparticles, designed to direct light in interesting and unusual ways. They offer fascinating possibilities of use in advanced components for optical applications such as cameras, microscopes and electronic displays. Usually, they tend to be viewed as stationary objects, with their use viewed as the ability to control and affect light. But here the researchers looked the other way, investigating how forces resulting from the change in light’s momentum could be used to control the meta-surface.

Like two billiard balls colliding

“According to Newton’s third law, for every action there is an equal and opposite reaction – this means that when light hits the meta-surface and is deflected in a new direction, the meta-surface is also pushed back into the other direction.. Imagine playing billiards, when two balls collide and bounce in different directions. In this case, the photons and the metasurface are like these two billiard balls “, explains Mikael Käll, professor in the physics department of the ‘Chalmers University of Technology, co-author of the article and responsible for the research project.

Carry other small items

“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 polarization of the light source, even more complex navigation would be possible, ”says Daniel Andrén, formerly in the Department of Physics at Chalmers and lead author of the ‘study.

Researchers also experimented with using metavhicles as carriers to push small particles around the tank. Metavehicles have been shown to be able to easily transport objects, including a microscopic polystyrene bead and a yeast particle through water. They even managed to push a dust particle 15 times the size of the metavhicle itself.

For the moment, the practical applications of this discovery may be far away. 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 the applications that guide this type of research, but the exploration of the different possibilities. In a number of different stages ahead, you never know what’s going to happen. But the fact that we have shown how metavehicles can be used as transporters is the most promising potential application initially, for example to move particles through cellular solutions, ”explains Mikael Käll.

More information on research

The project was funded by the Excellence Initiative Nano at Chalmers University of Technology, the Swedish Research Council and the Knut and Alice Wallenberg Foundation. For the project, a nanoprocessing was carried out at Myfab. The microscopic vehicles were made in Chalmers.