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.

Atomistic evaluation of tension–compression asymmetry in nanoscale body-centered-cubic AlCrFeCoNi high-entropy alloy

“…The vast majority of published literature report that the tension-compression asymmetry commonly exists in the nanoscale conventional metals and alloys [33][34][35][36][37][38][39][40] and inorganic composite materials. [41][42][43][44] As a novel type of metallic materials, research on the tension-compression asymmetry of HEAs is still in its initial stage. It is noteworthy that a recent experimental study [45] showed that an Al 0.3 CrFeCoNi HEA nanowire with FCC phase exhibits an apparent asymmetry in work hardening behavior between tension and compression.…”

Size-Dependent Response of CdSe Quantum Dots to Hydrostatic Pressure

“…Compared to sophisticated bulk system simulation techniques, the theory of the pressure dependence of the ground states and excited states of colloidal QDs is not well established, although several models have been proposed including direct atomistic simulations and continuum theories, , empirical force field and coarse-grained models, , and some first-principle calculations for smaller particles. ,, …”

“…33 To date, however, a systematic study to uncover the actual size dependence of the bulk modulus has not been undertaken, nor have there been any tests for the limit of applicability of bulk band structure concepts to the mechanics of nanocrystals. Compared to sophisticated bulk system simulation techniques, the theory of the pressure dependence of the ground states and excited states of colloidal QDs is not well established, although several models have been proposed including direct atomistic simulations and continuum theories, 34,35 empirical force field and coarse-grained models, 36,37 and some first-principle calculations for smaller particles. 27,38,39 A key limitation in earlier studies has been the widely used bulk approximation and use of the hydrogen/pseudo-hydrogen passivation technique.…”