Nanoscale materials often demonstrate mechanical properties following a "smaller is stronger" trend, which is of direct relevance to their broad applications including energy storage, nanoelectromechanical systems, and electronics. However,
mechanical characterization of individual nanostructures with dimensions at the lower nanoscale is highly challenging.
Here, by developing an ultrafast liquid-quenching methodology and performing insitu atomic-scale TEM, we report unusual room-temperature super-elongation without softening in face-centered-cubic silver nanocrystals with clean surfaces, where crystal slip serves as a stimulus to surface diffusional creep. This interplay
mechanism is shown to govern the plastic deformation of nanocrystals over a material-dependent sample diameter range between the lower and upper limits for nanocrystal stability by surface diffusional creep and dislocation plasticity, respectively. In addition, by creating a nanobattery inside a TEM, the strain
accommodation and volume expansion of individual nanowire electrodes were directly visualized during lithiation, which provides guidelines for design electrode with high resistance against mechanical degradation.