Size-dependent strengthening in nanowires: The roles of adatom diffusion and surface curvature on surface dislocation nucleation

Abstract

Understanding the factors governing incipient dislocation nucleation in nanoscale solids is crucial for predicting their mechanical strength and plasticity. While previous experimental studies of surface dislocation nucleation in metal nanowires have observed a strong nonlinear size effect, commonly referred to as “smaller is stronger”, the atomistic origins of this phenomenon remain unresolved. In this study, we investigate the hypothesis that surface curvature, in conjunction with surface adatom diffusion, can have a significant effect on size-dependent strengthening in metal nanowires. The hypothesis is supported by transmission electron microscopy images that reveal a definitive correlation between edge sharpness and nanowire diameter, with smaller diameters exhibiting more blunted edges. To do so, we develop a nucleation-based Kinetic Monte Carlo model that incorporates activation energy barriers for surface dislocation nucleation that are surface-curvature and adatom dependent. The model reveals that the activation energy reduction caused by adatoms is highly sensitive to the nanowire surface curvature, with blunted edges leading to higher activation energy for dislocation nucleation. Therefore, our model and results suggest that size-dependent surface curvature, in conjunction with the role of diffusing adatoms in assisting surface dislocation nucleation, can have a significant effect on size-dependent strengthening in metal nanowires.