Dislocation generation under extreme crystal conditions: small volume and high stress

The emerging nanoscale pristine crystals represent an extreme state of crystals: free of pre-existing dislocations and high surface-to-volume ratio. These crystals often show ultra-high strength and catastrophic plasticity. Here, we demonstrate two important surface dislocation sources underlying the ultra-high strength and dramatic plasticity, i.e., thermally activated nucleation (TAN) of surface dislocations and surface rebound sustained (SRS) generation of high-speed dislocations. The very first dislocation is created by TAN from surface and has been shown sensitive to surface stresses, leading to ultra-high crystal strength strongly dependent on sample size. However, subsequent dislocations governing significant plasticity are often generated in a strongly correlated SRS manner, i.e., under stresses that are a significant fraction of the ideal strength, the nucleated dislocation is accelerated to approach the sound speed and rebound into new dislocations when hitting free surfaces. The rebounded dislocations continue the relay until the sample is significantly relaxed. Our work bridges the experimental phenomena and atomistic insights by revealing dislocation physics on short timescale and calculating dislocation activation events under experiment-relevant conditions.