Unusual thermal transport in graphene / boron nitride single interface & superlattice tuned by interfacial roughness
Graphene combined with Boron Nitride is a superlattice that has a lot of potential in terms of tenability. There has been a lot of work that has gone into finding ways to tune the properties of this superlattice to improve its figure of merit. Interfacial roughness if strategically induced is thought to have the potential to increase the thermal conductivity without sacrificing any of the qualities of the superlattice. We perform equilibrium molecular dynamics via Green Kubo method on Graphene/Boron Nitride and study its thermal conductivity under the influence of various parameters that shape the superlattice and its properties. Green Kubo method involves generating the lattice structure and using a pair potential along with boundary conditions to implement equilibrium molecular dynamics. The simulation give us a heat current auto-correlation function (HCACF) which can be used to find the thermal conductivity of the system. Some important aspects that were found were the importance of ensuring a perfectly periodic lattice structure to make predictions of thermal conductivity as the phonons are extremely sensitive to any irregularities at the interface between two materials. The thermal conductivity of Graphene Boron Nitride superlattice is found to be dependent on the periodic length of the superlattice. It is found that at 5nm a critical periodic length is reached where a large amount of medium energy phonons scatter causing the thermal conductivity to drop quickly and then continue rising after that. In terms of single interface there is a relation between the ratio of height and width of the teeth that are induced in the interface to simulate roughness and the thermal conductivity of the material. At a ratio of about 0.25 a maximum thermal conductivity is reached for the Graphene-Boron Nitride superlattice. To enhance the thermal conductivity using interfacial roughness you would need to induce teeth that are 2.5Å in length in the interface which make it roughly the size of a unit cell hence not causing any disruptions to the phonons and at the same time increasing the thermal transport across the superlattice.
Ruan, Purdue University.
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