Decoupling the effects of ripples from tensile strain on the thermal conductivity of graphene and understanding the role of curvature on the thermal conductivity of graphene with grain boundaries

TL;DR

This study uses molecular dynamics simulations to decouple the effects of ripples, strain, curvature, and grain boundaries on graphene's thermal conductivity, revealing their individual impacts and dependencies.

Contribution

It introduces a novel approach to isolate ripple effects from strain and examines how curvature and grain boundary tilt angles influence thermal conductivity.

Findings

Ripples alone reduce TC by approximately 61%.

TC decreases linearly with curvature, depending on grain boundary tilt angles.

Both ripples and strain cause about 30% reduction in TC at higher strains.

Abstract

Ripples, curvature, and grain boundaries in graphene can significantly alter its thermal conductivity (TC), which is paramount in various applications including thermal management etc. In this study, we conducted extensive equilibrium MD simulations and used the Green-Kubo method to elucidate the impact of ripples on the TC of graphene and the impact of curvature and tilt angles characterizing a grain boundary (GB) on the TC of polycrystalline graphene. Although tensile and compressive strains have been known to control the amount of ripples, the effects of strain and ripple on the TC have not been decoupled. With the help of Green-Kubo simulations on larger graphene samples and simulations based on the spectral energy density method on smaller samples without ripples, we show that both samples show an approximately 30% decrease in TC between tensile strains 3% and 10% when ripples become negligible even in the larger sample. Between 0 and 3% strain, when both ripples and strains are present in the larger sample, we decouple the effect of ripples from strain on the TC and show that ripples alone reduce the TC of the larger unstrained sample by approximately 61%. We also present a unique technique to introduce curvatures in the graphene sheet containing GBs by performing MD simulations under NPT ensembles with a constant pressure of 200 bar along the x-axis. Our analysis suggests that the Green-Kubo TC linearly decreases with curvature; however, the rate of decrease depends on the tilt angles of the grain boundary. An analysis of the TC in graphene samples with GBs of varying tilt angles reveals that the TC strongly depends on the tilt angles. Thus, our research underscores the pivotal role of ripple, curvature, and GB in modulating the thermal conductivity of graphene.