Brittle fracture of ultrathin gold nanosheets induced by local phase change and energy dissipation

Metals with a face-centered cubic (fcc) structure, such as gold (Au), are generally known for their excellent ductility. However, in this study, we observed a novel brittle fracture behavior in ultrathin Au nanosheets with a thickness of approximately 15 nm and a diagonal length of up to 80 μm, synthesized via an aqueous solution method. Nanoindentation experiments on these nanosheets revealed a unique fracture pattern, characterized by crack propagation at angles of 120° from the indentation point. Molecular dynamics (MD) simulations replicated this unusual behavior, attributing it to a localized phase transformation from the fcc to hexagonal close-packed (hcp) structure under external stress. We hypothesize that this phase transition is initiated by stacking faults introduced during the nanosheet fabrication process. The observed brittle fracture is further influenced by an energy dissipation mechanism, as evidenced by the formation of slip lines around the fracture site. Our findings suggest that even in ductile metals like Au, brittle fracture can occur due to localized phase changes and energy dissipation. This study provides new insights into the mechanical behavior of ultrathin Au nanosheets, with implications for their application in nanoelectronics and other advanced technologies.