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 (κL) of monolayer SiC is two orders of magnitude lower than that of graphene. The low κL 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 κL 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 κL, 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 κL. 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.