Selective and Dynamic Control of Thermal Conduction in Graphene Heterostructures

Thermal transport is critical in engineering system design, as it directly affects the stability, durability, and efficiency of systems. To overcome new challenges in engineering design for high-power, flexible, and miniaturized devices, more effective, delicate, and specific control of thermal transport is required. As two-dimensional (2D) materials have attracted attentions due to their promises for innovative devices, demands for advanced control of their thermal transport have also arisen. Among 2D materials, graphene has been intensively studied for various applications due to its exceptional properties, and especially, its high thermal conductivity allows for effective investigation of various control effects. Therefore, graphene is selected for this study on thermal transport control. Selective and dynamic control of in-plane and cross-plane thermal transport are investigated for graphene and graphene heterostructures with Si and SiO2. For enhanced understanding of various control mechanisms, atomic vibrations and their fundamental properties are examined via molecular dynamics simulations.Structural design (substrate, defect, doping, etc.) and system conditions (temperature and pressure), which can affect scattering kinetics and interfacial transmission, are examined to achieve selective and dynamic thermal transport control. This study suggests the following findings: 1) Adding a substrate to freestanding graphene significantly reduces thermal conductivity by suppressing out-of-plane phonons, while the effect of another substrate is minimal. 2) Applying a mechanical pressure is very effective for anisotropic control, showing that change of cross-plane thermal transport is more than ten times larger than in-plane transport. 3) Reduction of nanosize structural defects (holes) on graphene is two-orders-of- magnitude larger than macroscale porous structure with the same porosity. Moreover, the hole arrangement in nanoscale systems can change the transport reduction and induce asymmetric thermal transport. 4) Si doping is another promising method of controlling in-plane conductivity by increased phonon scatterings, induced by both mass and interaction mismatch. 5) Both structural and point defects, created by holes and doping, enhance interfacial thermal transport due to the increase of cross-plane atomic interaction by in-plane structure weakening. Enhanced controllability of thermal transport from this research will allow for the development of innovative thermal engineering systems and improvement to energy conversion, storage, and heating/cooling systems.