Strain-dependent elastic asymmetry of alkylthiol-coated gold superlattices: An atomistic molecular dynamics study

Abstract

The elastic moduli of most materials in nature are commonly assumed to be identical (symmetric) under compressive and tensile loading. Here, we report an obviously asymmetric elastic property of alkylthiol-capped gold nanocrystal superlattices (NCSLs) in compression and tension computed from fully atomistic molecular dynamics simulations. Elastic asymmetry exhibits a clear trend of increasing with the increasing strain, and we attribute the strain-dependent elastic asymmetry to the variations of interaction between flexible ligand molecules during elastic deformations. In compression, ligand molecules sterically interact more with each other to continuously stiffen the NCSL, while in tension, they interact less and cause less stiffness. Unlike hybrid molecular materials, we find that the terminal groups of ligand molecules in the superstructure play only a minor role in determining the elastic asymmetry of gold NCSLs. In addition, the elastic asymmetry is observed to be essentially independent of ligand length and core size. These findings are expected to deepen our understanding of underlying asymmetric elastic properties of NCSL materials and may find technological applications in device technologies.