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, in collaboration with researchers from Utrecht, Brazil and Japan, created one on purpose. They stacked two sheets of molybdenum disulfide, a semiconductor crystal just three atoms thick, and rotated the top sheet by 2 degrees. The resulting pattern changes how the material interacts with light and repeats every 9 nanometers. Ten thousand of those repeats fit across the width of a single human hair.
The research, now published in Nature Physics, has possible applications in ultrasmall light sources and optical sensors.
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