Mechanical Behavior and Size–Dependent Strength of Small Noble-Metal Nanoparticles

Abstract

While metal nanoparticles are foundational to many advanced technologies, the instability of small particles limits their performance and lifetime. Extensive prior work has demonstrated size-dependent behavior, including “smaller-is-stronger”, “smaller-is-weaker”, and “liquid-like deformation”. However, mechanistic understanding of deformation processes has been hampered by the difficulty of characterizing nanoparticles as they fail. Here, we have compressed nanoparticles to failure with in situ transmission electron microscopy, linking their strength to direct observation of failure mechanisms. More than 250 tests, conducted on particles of Au, Ag, and Pt with sizes ranging from 3 to 130 nm, reveal a complex, non-monotonic dependence of strength on particle size. Deformation in larger particles (130 nm down to approximately 15 nm) is carried by dislocations nucleating from the surface. Without any observable change in mechanism, the nanoparticles first exhibit strengthening with decreasing size, reach a peak strength at around 30–60 nm, then show weakening. Deformation in intermediate-size particles (15 to approximately 5 nm) exhibits a mix of plasticity and diffusive deformation. Finally, the very smallest particles, with single-digit-nanometer sizes, exhibit homogeneous diffusive deformation that contradicts recent theories, and is instead well described by the zero-creep analysis. Overall, this work reveals the regimes and mechanisms underlying nanoparticle failure, across sizes and across materials.