Phonon thermal transport at the interfaces of graphene/vertically aligned carbon nanotubes /hexagonal boron nitride sandwich heterostructure

In this paper, molecular dynamics simulation is used to calculate the interfacial thermal resistance (ITR) of the graphene/carbon nanotubes/hexagonal boron nitride (Gr/CNTs/hBN) sandwich heterostructure, of which vertically aligned carbon nanotube (VACNT) arrays is covalently bonded to graphene and hexagonal boron nitride layers. We found that the ITR of the Gr/VACNT/hBN sandwich heterostructure is 1-2 orders of magnitude smaller than the ITR of the Gr/hBN Van der Waals heterostructure with the same plane size. It is observed that the covalent bonding effectively enhances the phonon coupling between Gr and hBN layers, resulting in an increase in the overlap factor of phonon density of state between Gr and hBN, thus reducing the ITR of Gr and hBN. In addition, the chirality, size (diameter and length) and packing density of sandwich-layer VACNT have an important influence on the ITR of the heterostructure. Under the same diameter and length of CNT, the ITR of the sandwich heterostructure with armchair-shaped VACNT is higher than that of the sandwich heterostructure with zigzag-shaped VACNT, due to the different chemical bonding of chiral CNT with Gr and hBN. When the armchairshaped CNT diameter increases or the length decreases, the ITR of the sandwich heterostructure tends to decrease. Moreover, the increase in the packing density of VACNT has also led to a continuous decrease in the ITR of the sandwich heterostructure, attributed to the extremely high intrinsic thermal conductivity of CNT and the increase of out-ofplane heat transfer channels. This work will help to understand the mechanism for ITR for multi-layer vertical heterostructures, and provide theoretical guidance for a new strategy to regulate the inter-layer thermal resistance of heterostructures by optimizing the design of sandwich layer thermal interface materials.