Investigating size effects in graphene-BN hybrid monolayers: a combined density functional theory-molecular dynamics study.

I S Oliveira,L D Machado,S Azevedo,J S Lima,A Freitas,C G Bezerra

doi:10.1039/d1ra00316j

Abstract

We combine Density Functional Theory (DFT) and classical Molecular Dynamics (MD) simulations to study graphene–boron nitride (BN) hybrid monolayers spanning a wide range of sizes (from 2 nm to 100 nm). Our simulations show that the elastic properties depend on the fraction of BN contained in the monolayer, with Young's modulus values decreasing as the BN concentration increases. Furthermore, our calculations reveal that the mechanical properties are weakly anisotropic. We also analyze the evolution of the stress distribution during our MD simulations. Curiously, we find that stress does not concentrate on the graphene–BN interface, even though fracture always starts in this region. Hence, we find that fracture is caused by the lower strength of C–N and C–B bonds, rather than by high local stress values. Still, in spite of the fact that the weaker bonds in the interface region become a lower fraction of the total as size increases, we find that the mechanical properties of the hybrid monolayers do not depend on the size of the structure, for constant graphene/BN concentrations. Our results indicate that the mechanical properties of the hybrid monolayers are independent of scale, so long as the graphene sheet and the h-BN nanodomain decrease or increase proportionately.

Highlights

Over the past few decades, two-dimensional (2D) materials have been an active research topic due to their exceptional physical and chemical properties, which promise applications in many modern technologies.[1]
We combined rst principles calculations and Molecular Dynamics (MD) simulations to investigate the mechanical properties of graphene
We combined Density Functional Theory (DFT) and MD simulations to investigate the mechanical properties of graphene sheets containing h-BN nanodomains

Summary

Introduction

Over the past few decades, two-dimensional (2D) materials have been an active research topic due to their exceptional physical and chemical properties, which promise applications in many modern technologies.[1]. An interesting subset of the BxCyNz sheets are those composed of h-BN nanodomains embedded within a larger graphene sheet (graphene–BN sheets) Structures of this type were synthetized for the rst time by Ci et al using the thermal catalytic CVD method.[22] The reported HRTEM images revealed that most samples had two or three layers, and included large hBN nanodomains with irregular geometric forms. Zhao et al investigated the mechanical properties of graphene–BN sheets using molecular dynamics (MD) simulations.[58] These authors considered different sizes, shapes, and amounts of h-BN nanodomains embedded in graphene sheets, and found that hybrid sheets displayed strong plasticity behavior. Our calculations show that the MD results are reliable, and that the mechanical properties do not depend on the scale of the considered structures, so long as the size of the h-BN nanodomain and the graphene sheet are increased by the same factor

Computational details and methods

Results and discussion

Conclusions