Strain-induced thermal switches with a high switching ratio in monolayer boron sulfide

Manipulating the thermal conductivity of materials and achieving a high thermal switching ratio is very important in fields such as thermal management and energy conversion. In this study, by utilizing first-principles calculations and semi-classical Boltzmann transport theory, we find the lattice thermal conductivity (kappa(l)) of monolayer boron sulfide (BS) can reach values as low as 0.11 Wm(-1) K-1 at room temperature, significantly lower than that of well-known two-dimensional materials with low thermal conductivity such as SnSe. This phenomenon is mainly caused by the strong lattice anharmonicity, which is primarily induced by the lone electron pairs. The effect of biaxial strain on kappa l is further investigated. It is found that a small strain of 2% can lead to a two orders of magnitude increase in kappa l. Moreover, this property remains stable within the strain range of 2%-7%, making it easier to achieve experimentally. The variation of kappa l with strain is mainly determined by the change in phonon lifetime, which is governed by the competition between the reduction of anti-bonding valence band states and the enhanced coupling between soft optical and acoustic phonons. Our results indicate that monolayer BS is a promising candidate material for thermal switches and energy conversion devices.