How a nanopattern traps the energy of light

Lay two pieces of fine mesh on top of each other and turn the top one slightly and a wavy periodic pattern appears. Physicists at the University of Twente, in collaboration with researchers from Utrecht, Brazil and Japan, applied the same effect at the nanoscale, using two semiconductor layers, each less than a nanometre thick. For the first time, they observed where such a pattern traps the energy of light. The research has possible applications in ultrasmall light sources and optical sensors.

You may have once tried taking a close-up picture of a computer screen and noticed a wavy, rippling effect. This optical effect occurs whenever two fine, repeating grids overlap and slightly misalign, such as when the pixel grid of your camera's sensor overlaps with the pixel grid of the screen.

Photographers know this wavy effect as a moiré pattern and usually try to get rid of it. Researchers at the University of Twente created one on purpose. They stacked two sheets of molybdenum disulphide, a semiconductor crystal just three atoms thick, and rotated the top sheet by two degrees. The resulting pattern changes how the material interacts with light and repeats every nine nanometres. Ten thousand of those repeats fit across the width of a single human hair.

Nanoscale landscape that traps excitons

When light hits a semiconductor, its energy can be absorbed into pairs of particles called excitons. These pairs largely determine how the material absorbs and emits light. Scientists have long suspected that a moiré pattern can trap excitons at fixed positions, which would offer a way to control light in a programmable grid.

But until now, nobody had been able to see this behavior directly. Optical measurements average over thousands of repeats of the pattern, and sharper microscopy methods only worked at extremely low temperatures. “With this new method, we have demonstrated that this moiré pattern indeed acts as a nanoscale landscape that guides and traps excitons in specific locations at room temperature,” says Pantelis Bampoulis, who led the research.

Different excitons settle in different places

First author Laurens Westenberg scanned the stacked layers with an atomically sharp needle while light of a precisely tuned colour illuminated them from below. At each point, the needle detected the tiny electric current generated by the light, allowing the team to map where light energy is absorbed.. The resulting maps show where each type of exciton sits, with nanometer precision.

The maps also revealed something unexpected: different kinds of excitons gather at different spots within the pattern. One group sits at the crossing points of the moiré lattice. Another settles in the regions in between, exactly where the first group is absent. Each exciton stays confined to a spot of roughly two nanometres.

Towards ultrasmall light sources

The method works at room temeperature and on real devices. That makes it a practical tool for designing components that use excitons. A moiré pattern offers a way to park the energy of light at chosen positions, spaced a few nanometres apart, simply by choosing the rotation angle. Westenberg: “Our results could help with the design of materials and devices that manipulate light absorption and electricity with much greater precision.”

About the researchers

Laurens Westenberg is the PhD student behind the experiments. He is supervised by Dr Pantelis Bampoulis, an expert in quantum materials that are only one or a few atomic layers thick. With microscopes that scan a surface atom by atom, Bampoulis’s group images how electrons and light behave in these materials. His research directions is funded by an NWO Vidi grant and an ERC grant. Westenberg and Bampoulis work at the MESA+ Institute for Nanotechnology of the University of Twente.

The study ‘Real-Space Imaging of Moiré-Confined Excitons in Twisted Bilayer MoS₂’ has been published in Nature Physics. University of Twente PhD student Laurens Westenberg performed the experiments. The research was a collaboration with Utrecht University, the Brazilian Center for Research in Physics (CBPF) and the National Institute for Materials Science (NIMS) in Japan. The theoretical model was developed at Utrecht University and the Brazilian Center for Research in Physics. The supporting boron nitride crystals were grown and characterised at the National Institute for Materials Science in Japan. This international collaboration between researchers in the Netherlands, Brazil and Japan grew out of QuMat (Materials for the Quantum Age), a Dutch Gravitation research programme that brings together scientists working on quantum materials.

DOI: 10.1038/s41567-026-03425-x