Effect of grain boundaries on thermal transport in bi-layer graphene nano-ribbons

Defects and grain boundaries (GBs) in graphene often form during its growth and have been extensively characterized experimentally. Moreover, in graphene with two or more layers, distinct defect profiles have been identified in different layers. Although these defects and GBs are known to reduce the thermal transport in monolayer graphene, their impact on the overall thermal transport in graphene with two or more layers remains obscure, especially when unique defect profiles exist in different layers. In this study, we employ molecular dynamics simulations to investigate the role of GBs in one of the bi-layer graphene nanoribbons (GNRs), which results in a moiré-like pattern on one side of the GB. We discovered that while the GBs in one of the bi-layer GNR sheets reduce the overall in-plane thermal conductivity, κ, the reduction is mitigated by the pristine layer due to the interlayer van der Waals interaction. By closely examining different phonon modes in individual layers, we elucidate the κ reduction mechanisms in each layer. Our findings offer valuable insights into thermal engineering in graphene-based heterostructures as well as into exotic graphene bi-layer structures, such as those with moiré patterns.