Structural evolution and fusion behavior of gold supercrystals under stress : Insights from atomistic simulations

Stress-driven assembly and sintering of nanocrystal (NC) supercrystals is an effective mechanical method for fabricating ordered 1D nanostructure arrays. Here, we preform atomistic molecular dynamics simulations for alkylthiol-coated gold supercrystal to reveal its structural evolution and fusion behavior under high-pressure-induced stress. On initial hydrostatic compression, the supercrystal reduces lattice dimension nonlinearly with pressure and displays a reversible pressure-dependent change of interparticle distance, in good agreement with the experiment. Subsequently, the deviatoric compression results in a distorted and noncubic superstructure, where an unexpected structural hysteresis is observed during a compression-release cycle. These structural changes are explained in terms of the molecular conformation of passivating ligands as well as its variations caused by the change in the external stress. In particular, when the pressure exceeds a threshold, neighboring NCs start to contact one another and consolidate into numerous dimers and trimers, which further evolve into short nanorods and finally lead to an irreversible formation of stable nanowires. The structural and stress change in the gold NCs during the compression process are also analyzed. This work is expected to provide useful insights into the mechanical response of supercrystals subjected to an external stress.