The disparate effect of strain on thermal conductivity of 2-D materials

Thermal transport in 2-D (dimensional) structures is highly susceptible to external perturbations such as strain, owing to their high surface-to-volume ratio. In this study, we investigate the influence of strain on the thermal conductivity of flat (graphene and hexagonal boron nitride), buckled and puckered (molybdenum disulfide and black phosphorous) 2-D materials. Unlike bulk materials where the thermal conductivity reduces with strain, the thermal conductivity of 2-D materials under strain is observed to be unique and dependent on the material considered. To understand such diverse strain-dependent thermal conductivity in 2-D materials, the phonon mode properties are calculated. It was observed that the strain softens the longitudinal mode (LA), whereas the out-of-plane acoustic mode (ZA) undergoes stiffening albeit various extents. In flat 2-D materials, the dispersion of ZA mode is linearized under strain while it tends to linearize in buckled and puckered structures. The variation in the phonon group velocity of ZA mode coupled with the anomalous behavior of the phonon lifetime of acoustic modes results in a diverse strain dependence of the thermal conductivity of 2-D materials. Our findings offer insight into the influence of strain of 2-D materials and will be helpful in tailoring the thermal properties of these materials for various applications such as nanoelectronics and thermoelectric devices.