Highly in-plane anisotropy of thermal transport in suspended ternary chalcogenide Ta₂NiS₅

Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional (2D) materials are considered to have broad prospects in solving the energy dissipation problem. Herein the thermal transport of a typical 2D ternary chalcogenide Ta₂NiS₅ is investigated. For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta₂NiS₅ flakes through Raman thermometry. For 7-nm-thick Ta₂NiS₅ flakes, the ${\kappa }_{\mathrm{z}\mathrm{i}\mathrm{g}\mathrm{z}\mathrm{a}\mathrm{g}}$ is 4.76 W·m⁻¹·K⁻¹ and ${\kappa }_{\mathrm{a}\mathrm{r}\mathrm{m}\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{i}\mathrm{r}}$ is 7.79 W·m⁻¹·K⁻¹, with a large anisotropic ratio ( ${\kappa }_{\mathrm{a}\mathrm{r}\mathrm{m}\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{i}\mathrm{r}}/{\kappa }_{\mathrm{z}\mathrm{i}\mathrm{g}\mathrm{z}\mathrm{a}\mathrm{g}}$) of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes. Moreover, the thickness dependence of thermal anisotropy is also discussed. As the flake thickness increases, the ${\kappa }_{\mathrm{a}\mathrm{r}\mathrm{m}\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{i}\mathrm{r}}/{\kappa }_{\mathrm{z}\mathrm{i}\mathrm{g}\mathrm{z}\mathrm{a}\mathrm{g}}$ reduces sharply from 1.64 to 1.07. This could be attributed to the diversity in phonon boundary scattering, which decreases faster in zigzag direction than in armchair direction. Such anisotropic property enables heat flow manipulation in Ta₂NiS₅ based devices to improve thermal management and device performance. Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides, along with significant guidance to develop energy-efficient next generation nanodevices.