Decoupling ripple and tensile strain effects and understanding curvature effects on thermal conductivity of polycrystalline graphene

Ripples, curvature, and grain boundaries in graphene can significantly alter its thermal conductivity (TC), which is paramount in various applications including nanoelectronics and thermal management. In this study, we conducted extensive equilibrium molecular dynamics 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 systems of size 150×100 Å2 and simulations based on the spectral energy density (SED) method on smaller systems without ripples of size 31×26 Å2, we show that both systems show an approximately 30% decrease in TC between tensile strains 3% and 10% when ripples become negligible even in the larger system. Between 0% and 3% strain, when both ripples and strains are present in the larger system, we decouple the effect of ripples from strain on the TC and show that ripples alone reduce the TC of the larger unstrained system by approximately 61%. We also present a unique technique to introduce curvatures in the graphene sheet containing GBs by performing molecular dynamics (MD) simulations under isothermal-isobaric (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 systems with GBs of varying tilt angles reveals that the TC strongly depends on the tilt angles. In summary, our research underscores the pivotal role of ripple, curvature, and grain boundary in modulating the thermal conductivity of graphene with and without the grain boundary.