New material reflects different color by deforming it

Scientists at UC Berkeley in California have developed ultra-thin material that reflects different colors when bent. The silicon film could one day be used to detect virtually invisible cracks in bridges, buildings or airplanes, for example.

The film uses a new approach to color change. This method is based on modifying the surface to reflect different visible wavelengths rather than changing the chemical composition of a material. In the 120nm thick semiconductor material, ridges and rods are etched thinner than a single light wave. Each obstacle in the film is designed to reflect a particular wavelength of light. By bending or stretching the film, the film reflects other colors.

The first piece of material was only one square centimeter in size, but one of the researchers says that there are already several possibilities to also produce larger surfaces of the material within the existing semiconductor industry. Once that is successful, the researchers hope to find applications. They initially think of sensors that change color in the event of metal fatigue, for example, but the entertainment industry and security sector could also make use of them.

This way of ‘making’ different colors also occurs in nature. Certain butterflies and beetles change color this way. The material developed by the scientists reflects up to 83 percent of the incoming light and changes color at a bend of 25nm. The color shift in the prototype goes from green to yellow, orange and red over 39nm of wavelengths. Further research should increase the number of colors to be displayed.

The study’s paper will be online Monday on the site of the scientific journal Optica.