Direct observation of autonomous self-healing in silver

Although the concept of self-healing has undergone a recent resurgence of interest in polymers and other soft materials, it is extremely rare for metal solids to autonomously self-repair structural damage without any external trigger. Here, we report on the direct in situ observation of such an autonomous solid-state self-healing behavior in nanoscale silver (Ag) by utilizing atomic-resolution transmission electron microscopy (TEM). Two representative kinds of structural damage—both nanopores and nanocracks—are observed to undergo automatic self-repair at room temperature and well below (down to 173 K) without any external intervention. Importantly, such an autonomous self-healing phenomenon does not occur in gold (Au) at room temperature, as it is hindered by the stronger Au-Au bonding resulting from the known relativistic effect. A combination of atomistic imaging and molecular dynamics simulation unravels that the self-healing process is accomplished through surface-mediated diffusion of Ag atoms as driven by chemical potential imbalance due to the Gibbs-Thomson effect.