Familiar materials will act differently at the smallest scales. Notably, diamonds—typically hard and brittle—grow strangely soft at the nanoscale. After years of not quite understanding why, a team of physicists finally managed to decode this behavior.

Using a custom-built electron microscope, researchers found that tiny diamonds had a relatively weak chemical bond between their surface layer and their core. Placing nanodiamonds under pressure concentrates the strain at an intermediate region between the diamond’s surface and the core. As a result, the tiny diamond doesn’t fracture but instead reacts like a flexible material, “enabling elasticity that is almost impossible in bulk diamond,” the researchers reported in a recent Physical Review X paper on the findings.

“This hidden mechanism may play a role in the elasticity of brittle materials and suggest the archetype of rigidity diamond can have its mechanical properties tuned at nanoscale,” the team, led by researchers at Zengzhou University and the…