Predicting Phonon Thermal Transport in Strained Two-dimensional Materials: Graphene, Boron Nitride, and Molybdenum Disulfide

Despite the extensive research done on two-dimensional materials in recent years, little is still known about the physics of thermal energy carriers (phonons) at this low dimensionality, especially when these materials are stretched. In this work, we apply molecular dynamics simulations to estimate phonon relaxation times and thermal conductivities of strained samples of single-layer graphene, boron nitride, and molybdenum disulfide. Our results reveal that the thermal response of these 2D materials to tensile strain is considerably different, despite the similarities of their lattice structures. On the one hand, the thermal conductivity of boron nitride monotonically increases until 18% of strain is applied, approximately doubling the conductivity of an unstrained sample. On the other hand, the thermal conductivity of graphene first increases by roughly 30% until 8% of strain is applied, and then it sharply decreases for higher percentages of strain. In contrast, the conductivity of molybdenum disulfide drops dramatically in response to percentages of strain as small as 2%. These thermal responses are addressed here in the context of the phonon properties of these materials, with particular emphasis on the role of the acoustic phonon modes.