Nanopore-Induced Thickness Independence of In-Plane Thermal Transport in Few-Layer Graphitic Carbon Nitride

Although in-plane thermal transport in many two-dimensional (2D) materials exhibits pronounced thickness dependence, it remains unclear whether this behavior persists in intrinsically porous 2D systems. In this work, we employ a scalable, high-accuracy atomistic simulation framework that integrates an intralayer machine-learned interatomic potential with a registry-dependent interlayer interaction model to investigate in-plane thermal transport in porous 2D graphitic carbon nitride (g-C3N4). Unlike typical layered materials such as graphene, h-BN, and MoS2, which often exhibit pronounced thickness-dependent thermal transport, g-C3N4 displays nearly unchanged in-plane thermal conductivity from monolayer to trilayer. Heat-current vector analysis reveals that intrinsic nanopores and their boundaries strongly disrupt the in-plane heat-flow network, thereby confining the mean free paths of low-frequency phonons down to the nanometer scale. Consequently, the additional interlayer coupling introduced by increasing layer number exerts only a limited influence on the overall in-plane thermal transport. These results clarify the physical origin of thickness-insensitive in-plane thermal transport in porous 2D materials and provide a mechanistic basis for thermal management through nanopore engineering.