Using light to drive more sustainable chemical reactions
Many chemical reactions require energy, which is often supplied in the form of heat. Photocatalysis offers another possibility: using light to provide the energy needed for a reaction. This has the potential to make chemical processes more sustainable, particularly if light can deliver energy precisely where it is needed.
That precision is important because different catalytic materials respond to different colors of light. Ideally, you would therefore like to choose a particular color and send it directly to the material where a reaction should take place. This could eventually allow different light-driven reactions to be controlled within the same small system.
A flexible way to guide light
Achieving that level of control at very small scales is difficult. Light from a laser needs to enter an extremely thin structure that can guide it to the desired location.
Existing solutions usually rely on tiny structures that are carefully designed and manufactured for a particular wavelength and direction. Once they have been made, their properties are difficult to change.
The AMOLF researchers found a simpler and more flexible approach. They placed glass spheres measuring about five micrometers in diameter on an extremely thin layer of silicon nitride, a material made of silicon and nitrogen. This 50-nanometer-thick layer acts as a pathway for light. When the researchers aim a laser at the edge of a glass sphere, some of the light enters this layer and can then travel through it to another location. This is important because it allows the researchers to deliver light to a specific place, for example to particles where a chemical reaction should take place.
Choosing where the light goes
Up to 50 percent of the incoming light could be transferred into the silicon nitride layer. By changing the position of the laser beam, the researchers could also select which color of light was transferred most efficiently. In their experiments, they shifted colors from green to deep red.
Moving the laser spot around the edge of the glass sphere also allowed the researchers to determine the direction in which the light traveled. This means that both the color and direction can be adjusted without having to manufacture a new structure.
A first step toward photocatalysis
As a first demonstration, the researchers used the glass spheres to direct light toward tiny gold cubes placed on the silicon nitride layer. They showed that the guided light could interact with these particles. This is an initial step toward using the technique for photocatalysis, where precise delivery of the right color of light could help make reactions more efficient.
The ability to control light in such a flexible way could also be useful in semiconductor applications and in compact sensors that use light to identify substances.
Learn more
If you have any questions about this research, contact AMOLF group leader Erik Garnett at e.garnett@amolf.nl.
The paper ‘From Free Space to Guided Modes: Tunable and Directional Coupling with Microsphere Resonators’ was published in ACS Photonics on August 13th, 2026.
