Extreme Thermal Insulation and Tradeoff of Thermal Transport Mechanisms between Graphene and WS2 Monolayers

Abstract Controlling and understanding the heat flow at a nanometer scale are challenging, but important for fundamental science and applications. Two‐dimensional (2D) layered materials provide perhaps the ultimate solution for meeting these challenges. While there have been reports of low thermal conductivities (several mW m −1 K −1 ) across the 2D heterostructures, phonon‐dominant thermal transport remains strong due to the nearly‐ideal contact between the layers. Here, this work experimentally explores the heat transport mechanisms by increasing the interlayer distance from perfect contact to a few nanometers and demonstrates that the phonon‐dominated thermal conductivity across the WS 2 /graphene interface decreases further with the increasing interlayer distance until the air‐dominated thermal conductivity increases again. This work finds that the resulting tradeoff of the two heat conduction mechanisms leads to the existence of a minimum thermal conductivity at 2.11 nm of 1.41 × 10 −5 W m −1 K −1 , which is two thousandths of the smallest value reported previously. This work provides an effective methodology for engineering thermal insulation structures and understanding heat transport at the ultimate small scales.