Nonmonotonic strain dependence of lattice thermal conductivity in monolayer SiC: a first-principles study

Abstract

An increasing number of two-dimensional (2D) materials have already been achieved experimentally or predicted theoretically, which have potential applications in nano- and opto-electronics. Various applications of electronic devices are closely related to their thermal transport properties. In this work, the strain dependence of phonon transport in monolayer SiC with a perfect planar hexagonal honeycomb structure is investigated by solving the linearized phonon Boltzmann equation. It is found that the room-temperature lattice thermal conductivity (κ_L) of monolayer SiC is two orders of magnitude lower than that of graphene. The low κ_L is due to small group velocities and short phonon lifetimes, which can also be explained by the polarized covalent bond due to large charge transfer from Si to C atoms. In a considered strain range, it is proved that the SiC monolayer is mechanically and dynamically stable. With increased tensile strain, the κ_L of the SiC monolayer shows an unusual nonmonotonic up-and-down behavior, which is due to the competition between the change of phonon group velocities and phonon lifetimes of low frequency phonon modes. At low strain values (<8%), the phonon lifetime enhancement induces the increased κ_L, while at high strain values (>8%) the reduction of group velocities as well as the decrease of the phonon lifetimes are the major mechanisms responsible for decreased κ_L. Our works further enrich the studies on the phonon transport properties of 2D materials with a perfect planar hexagonal honeycomb structure, and motivate further experimental studies.