Plastic deformation in nanodiamonds.

Diamond, composed of sp³ covalent carbon bonds, is renowned for its exceptional hardness, thermal conductivity, and wide bandgap, yet its intrinsic brittleness severely limits deformation and processing. Here, we report an amorphization-mediated ultralarge plasticity in nanodiamonds using a custom-designed in-situ transmission electron microscopy mechanical holder. Unlike conventional mechanisms such as dislocation motion or crystalline phase transformation, the deformation is governed by the formation of an interconnected amorphous carbon network that accommodates stress and enables cooperative grain rotation and sliding. This amorphization-mediated plasticity allows nanodiamonds to sustain compressive strains exceeding 90% without fracture. A distinct size-dependent transition is identified: ultralarge plasticity occurs only below ~13 nm, while larger diamonds deform in a brittle manner. This work provides critical insights into nanoscale mechanics and offering exciting opportunities for diamond-based nano-manufacturing, strain engineering, and advanced quantum or electronic device applications.