Low thermal conductivity and interface thermal conductance in SnS2

After the discovery of graphene, there have been tremendous efforts in exploring various layered two-dimensional (2D) materials for their potential applications in electronics, optoelectronics, as well as energy conversion and storage. One of such 2D materials, $\mathrm{Sn}{\mathrm{S}}_{2}$, which is earth abundant, low in toxicity, and cost effective, has been reported to show a high on/off current ratio, fast photodetection, and high optical absorption, thus making this material promising for device applications. Further, a few recent theoretical reports predict high electrical conductivity and Seebeck coefficient in its bulk counterparts. However, the thermal properties of $\mathrm{Sn}{\mathrm{S}}_{2}$ have not yet been properly explored, which are important to materialize many of its potential applications. Here, we report the thermal properties of $\mathrm{Sn}{\mathrm{S}}_{2}$ measured using the optothermal method and supported by density functional theory (DFT) calculations. Our experiments suggest very low in-plane lattice thermal conductivity ($\ensuremath{\kappa}=3.20\ifmmode\pm\else\textpm\fi{}0.57\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{--1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{--1}$) and cross-plane interfacial thermal conductance per unit area $(g=0.53\ifmmode\pm\else\textpm\fi{}0.09\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{--2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{--1})$ for monolayer $\mathrm{Sn}{\mathrm{S}}_{2}$ supported on a $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ substrate. The thermal properties show a dependence on the thickness of the $\mathrm{Sn}{\mathrm{S}}_{2}$ flake. Based on the findings of our DFT calculations, the very low value of the lattice thermal conductivity can be attributed to low group velocity, a shorter lifetime of the phonons, and strong anharmonicity in the crystal. Materials with low thermal conductivity are important for thermoelectric applications as the thermoelectric power coefficient goes inversely with the thermal conductivity.