Ultralow lattice thermal conductivity of Gr/h-BN heterostructure using controlled twist engineering

Two-dimensional nanomaterials like graphene and hexagonal boron nitride (h-BN) offer superior electronic properties for future nanoelectronics [1], spintronics [2] and energy applications. When the two materials are combined together to form a van der Waals heterostructure [3], the resulting material offers novel thermal characteristics. In this work, we focus on the electronic, and thermoelectric properties of the Gr/h-BN van der Waals heterostructure in the presence of various twisting angles using on the First-principles based calculations. To sustain the structure stability, we have studied the optimized rotation angles, namely q = 0^o, 16.10^o, 21.79^o, 38.21^o, 43.90^o and 60^o. The material changes from semi-metallic to semiconducting nature at 21.79^o and 38.21^o twisting angles, respectively. Using semiclassical Boltzmann transport approach, Seebeck coefficient, electrical conductivity and power factor at twist angles of 0^o, 21.79^o, 38.21^o, and 60^o are found to be much higher than the other configurations. Moreover, at the 60^o twisting angle, the Power Factor in the n-type dopants can reach upto 1.37×10¹¹ W/msK². The lattice thermal conductivity at room temperature is found to be very low in 16.10^o, 21.79^o, 43.90^o and 38.21^o rotation angles. An ultralow lattice thermal conductivity with a value of 0.095 W/m K at 300K has been observed for 21.79^o rotation angle, which is lower than our other rotation angles because of the very low group velocity (22.1 ×10³ Km/s) and short phonon lifetime (0.18 ps) at 21.79^o angle. The high thermoelectric performance results from an ultralow thermal conductivity arising due to the strong lattice anharmonicity. These results can have a significant impact on the synthesis of high performance thermoelectric materials based on twisted Gr/h-BN heterostructure.