UNUSUALLY beautiful and uniform cracks that form in high-tech materials could be used to manufacture micro-patterned surfaces.
Joël Marthelot of ESPCI ParisTech in France and his colleagues noticed the cracks when studying thin films of silicate materials, which are used as a coating inside lasers.
If the coating doesn't quite stick to the surface below, cracks can form that spiral around a central point or that etch out regular rows of crescents. Optical effects caused by the film lifting from the surface produce watercolour-like hues.
Other researchers had seen these cracks in similar materials, but no one had studied how they formed. Investigating further, Marthelot and his colleagues realised that a combination of elastic energy within the film and the process of peeling away from the underlying surface makes an initial crack replicate itself an interval that depends on the thickness of the film (Physical Review Letters, doi.org/vb5).
These regular patterns could be useful in processes such as creating microscopic channels for transporting liquids. "Usually fracture is seen as failure and something you have to avoid," says Marthelot, who is now at the Massachusetts Institute of Technology. "We can think about using such cracks as tools to make patterns at small scales."
"It's a nice piece of work, the pictures are beautiful," says Nicolas Vandenberghe of Aix-Marseille University in France. "Maybe cracks will become a useful process to manufacture or design specific things."
This article appeared in print under the headline "Spiral cracks are a feature, not a flaw"
Correction, 28 August 2014: When this article was first published, the affiliation for Joël Marthelot was incorrect.
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