A nanoscale chameleon: how stretchable nanostructures shift color
Drawing inspiration from kirigami—the art of cutting and folding paper—researchers at the University of Amsterdam have created a material that visibly changes color simply by stretching. Their work, published in ACS Photonics, demonstrates a metamaterial whose reflected hue evolves as its geometry is deformed.
Color by structure
In most everyday materials, color arises from the substance itself—pigments or dyes dictate what we see. Once the material is made, that color is fixed. The new material, however, derives its color from its internal architecture. This phenomenon, known as structural color, offers a major advantage: the color can be switched at will by altering the structure.
These metamaterials are composed of features far smaller than a human hair. Their color depends on the arrangement and shape of these subwavelength elements, echoing kirigami’s emphasis on precise patterns. When the material is stretched, its nanoscale patterns reorient and move, changing how light reflects off the surface. The result is a smooth color transition—from green through yellow to red—as the material is elongated. It’s like a chameleon skin that responds to motion rather than chemistry.
Mechanical meets optical design
The path to this material wasn’t straightforward. Lead author Freek van Gorp recalls that silicon’s brittleness at larger scales posed a challenge. Early attempts to place tiny silicon particles on a flexible substrate ran into new problems, because the substrate altered the system’s behavior. The turning point came with the idea of removing the substrate altogether and crafting a thin, patterned silicon mesh. This realization allowed the material to be both flexible and functional, marrying optical metasurfaces with mechanical metamaterials in a single, cohesive design. That fusion is what enables the observed tunable color effect.
According to Jorik van de Groep, head of the 2D nanophotonics lab where the research took place, the key innovation lies in multifunctionality. By nanopatterning the slender silicon membrane, the team made it serve a dual role: a mechanical metamaterial that controls internal motion and a resonant optical metasurface that governs light scattering, together producing the adjustable structural color.
From theory to practice
Having completed the design in silico, the researchers are now transitioning to real-world fabrication. They are constructing a flexible metasurface in the cleanroom facilities at AMOLF to move from simulation to a tangible device. Demonstrating that light can be tuned through motion rather than chemistry paves the way for practical applications. In the near future, we might see tunable color coatings, smart sensors, and light-weight optical components that adapt their appearance or function in response to their surroundings.
