Negative correlation between cross-plane bonding strength and in-plane thermal transport in bent van der Waals materials

Strain engineering stands out as a promising avenue for manipulating the physicochemical characteristics of two-dimensional (2D) van der Waals (vdW) materials. Amidst the flourishing investigations into the modulation of electronic band structures, the influence of elastic strain on the evolution of phonon spectra and, consequently, thermal transport has garnered comparatively less attention. Yet, this facet offers a realm of intricate physics and engineering possibilities. Bending, a process that couples in-plane (IP) and cross-plane (CP) motion, provides a unique opportunity to investigate the influence of elastic anisotropy on the thermal properties of inhomogeneous strain-modulated 2D materials. Here we studied the effects of CP bonding on the IP thermal conductivities of a model layered material using molecular dynamics simulation. Notably, our findings unveiled an intriguing negative correlation between CP bonding strength and IP thermal conductivity while keeping IP bonding constant. This can be attributed to the heightened stress gradient spanning across multiple layers due to the pronounced CP bonding, which in turn, engenders a broadened phonon spectrum, and eventually stronger phonon scattering. Our work sheds light on the intricate interplay between CP bonding and thermal transport in bent vdW materials, offering insights extendable to the broader family of 2D materials.