Principles and Mechanisms of Strain-Dependent Thermal Conductivity of Polycrystalline Graphene with Varying Grain Sizes and Surface Hydrogenation

Abstract

In this paper, the thermal conductivities (κ) of polycrystalline graphene (PG) with varying average grain size are investigated using reverse nonequilibrium molecular dynamics method. Due to the presence of grain boundary (GB), the κ of PG is found to depend on the average grain size as well as in-plane strain and hydrogenation coverage. The principles and mechanisms for the change of κ with in-plane strain and surface hydrogenation are interpreted combining the thermal transport theory and phonon density of states (PDOS) analysis. The thermal property of PG under tension is found to be related with the average stress in PG as a result of the suppression of mean free path (MFP) and the softening of phonon modes. PG with fine grains exhibits more reduction of κ than the PG with coarse grains does under the same tensile strain due to the more stress concentration at GBs. The mechanism is also revealed for the size effect on the thermal property of PG under compression. Additionally, the dependency of κ on the surface hydrogenation of PG is investigated, and an unexpected two-stage evolution of κ with hydrogenation coverage is interpreted preliminarily from the circumference and arrangement of functionalized domains. The negative effect of GB on thermal conductivity is weakened significantly under full hydrogenation. Furthermore, the coupling effect between hydrogenation and strain on the κ of PG is revealed, and the thermal conductivity of PG becomes insensitive to the in-plane strain under higher hydrogenation. Our results provide new insights into the role of GB on the thermal manipulation of PG and offer theoretical guidelines for the design of graphene-based flexible devices in thermoelectric and thermal management applications.

Efficient modulation of thermal transport in two-dimensional materials for thermal management in device applications

“…However, when the GB energy is high enough, κ is more sensitive to the grain size than the GB energy. 101 In addition, when grains and GBs are present in 2D materials, some modulation means, such as strain, 96 doping, 102 and tilt angle, 103 will also have different effects on its thermal transport properties than in the single crystal case.…”

SISSO-assisted prediction and design of mechanical properties of porous graphene with a uniform nanopore array

“…The interactions between carbon atoms are described by the adaptive intermolecular reactive empirical bond order (AIR-EBO) potential, 31 which has been widely used and conrmed in graphene-based material systems. [32][33][34] The original parameter of the carbon-carbon cutoff distance in the potential is modied to be 2.0 Å to avoid a known non-physical post-hardening phenomenon. 35,36 The timestep is set at 0.5 fs during the overall simulation.…”

Defects in graphene-based heterostructures: topological and geometrical effects

“…These studies and related discoveries raised a series of questions for material physics research, and also provided opportunities for the preparation and design of micro–nano materials and structures. In 2018, A. R. Wei 85 used a reverse nonequilibrium molecular dynamics method to study the effect of the grain boundary and hydrogenation on the strain-dependent thermal conductivity of hydrogenated polycrystalline graphene under the condition of a strain field. The results showed that the thermal properties of hydrogenated polycrystalline graphene under tension load were related to the average stress in the hydrogenated polycrystalline graphene due to the softening of the phonon modes.…”

“…The results showed that the thermal properties of hydrogenated polycrystalline graphene under tension load were related to the average stress in the hydrogenated polycrystalline graphene due to the softening of the phonon modes. 85 This could be attributed to the fact that both hydrogenation and oxidation will gradually change the material from a honeycomb to a diamond-like structure as result of the hybridization transition from sp 2 to sp 3 , while the introduction of grain boundary will only lead to the distortion of sp 2 hybridization. 86 Also in 2018, using molecular dynamics, the coupling effects of an external field (temperature and strain) and internal field (longitudinal and transverse defects) on the mechanical properties of Gr/h-BN–Cu heterostructures were investigated by L. Fan et al 87 As a result, atoms near the defect are more likely to escape covalent bond forces when the temperature increases.…”