Deformation behavior of nanoporous gold nanoparticles during compression

In this experimental-computational study, we propose a novel method to study the inhomogeneous deformation of nanoporous Au structures and quantifying locally their deformation. By combining the dewetting method and dealloying of Ag-Au alloys, we fabricated sub-micrometer scale hemispherical nanoporous Au nanoparticles (NPG-NPs). The formed nanoparticles have an average ligament diameter of 13 nm and diameter ranging between 200 and 800 nm. A few grain boundaries, mostly of twin type, were found within the NPG-NPs. Under compression with a flat diamond punch, the load-displacement curves exhibited linear increase, up to a certain compression depth, above which a significant rise in the slope was identified. Molecular dynamics (MD) simulations of NPG-NPs with various sizes, porosities, and ligament diameters were conducted. The simulated load-displacement curves closely matched the experimental ones. With the help of the MD simulations, we identified the dependencies of the NPG-NP mechanical properties on their geometry. To better understand how to quantify these dependencies, we analyzed the densification profiles during the deformation. We found that the densification is inhomogeneous and localized beneath the compressing punch. In combination with the dislocation density profiles, we correlated the densification region with the mean-free path of dislocations and their depletion due to the high surface-to-volume ratio. We showed that the slope increase in the load-displacement curves is attributed to the interaction between the densified region (dislocation structure) and the substrate. Finally, we propose a model for the inhomogeneous deformation, enabling to determine the contact stresses in the experiments.