Structural dynamics of polycrystalline graphene

TL;DR

This study investigates the mechanical and dynamic properties of polycrystalline graphene through simulations, revealing diffusive behaviors of cell dimensions and linking defect density to diffusion coefficients, which inform its mechanical response.

Contribution

It introduces a detailed analysis of the dynamic fluctuations in polycrystalline graphene's simulation cell and connects these to physical properties and defect structures.

Findings

Both area and aspect ratio show diffusive behavior over short times.

Long-term fluctuations in area are bounded, but aspect ratio fluctuations are unbounded.

Diffusion coefficients relate to defect density and can predict mechanical responses.

Abstract

The exceptional properties of the two-dimensional material graphene make it attractive for multiple functional applications, whose large-area samples are typically polycrystalline. Here, we study the mechanical properties of graphene in computer simulations and connect these to the experimentally relevant mechanical properties. In particular, we study the fluctuations in the lateral dimensions of the periodic simulation cell. We show that over short time scales, both the area A and the aspect ratio B of the rectangular periodic box show diffusive behavior under zero external field during dynamical evolution, with diffusion coefficients DA and DB that are related to each other. At longer times, fluctuations in A are bounded, while those in B are not. This makes the direct determination of DB much more accurate, from which DA can then be derived indirectly. We then show that the dynamic behavior of polycrystalline graphene under external forces can also be derived from DA and DB via the Nernst-Einstein relation. Additionally, we study how the diffusion coefficients depend on structural properties of the polycrystalline graphene, in particular, the density of defects.