Anisotropic In-Plane Thermal Conductivity of Freestanding Few-Layer ReS2

ReS2 is a low-symmetry transition-metal dichalcogenide exhibiting strong in-plane anisotropy, weak interlayer coupling, and stacking-dependent physical properties. While anisotropic thermal conductivity has been reported in bulk ReS2, experimental studies on stacking-dependent thermal conductivity and its thickness evolution in the few-layer regime remain largely unexplored. Here, we extract the thermal conductivity of freestanding, few-layer ReS2 samples (thickness <10 nm) using polarization-resolved optothermal Raman thermometry. All ReS2 samples show pronounced in-plane anisotropic thermal conductivity. Notably, the ∼3.5 nm AA-stacked flake shows higher thermal conductivity than the AB-stacked flake of the same thickness, highlighting the influence of stacking order on phonon transport. The in-plane thermal conductivity displays a nonmonotonic dependence on thickness over the ∼2.5–8 nm range, which is supported by density functional theory calculations. These findings provide key insight into anisotropic phonon transport in low-symmetry 2D materials and highlight the potential of few-layer ReS2 for nanoscale thermal management and thermoelectric applications.