Chemistry in Pictures: Spotting spirals

After seeing these patterns under a microscope, Yilin Wong changed the focus of her PhD research. Initially, the University of California, Los Angeles, student was studying ultrasensitive thermometry and conducting experiments that required anchoring DNA molecules to this metal film. After she left a mild acid on the film overnight as part of the experiment, she noticed tiny dots. Under a microscope, those dots turned out to be wavy, spiraling, and radial patterns etched into the germanium wafer that supported the metal film. Wong decided she should pivot her PhD research to pattern formation in complex systems.

She and her adviser, Giovanni Zocchi, still don’t know exactly why these patterns arise, but the team suggests that the process involves two factors: the metal film catalyzing the etching and mechanical stresses in the film that speed up or slow down the catalysis in certain areas. The tiny shapes are about 200–1000 µm wide.

Credit: Yilin Wong

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