Anisotropic In-plane Thermal Conductivity of Freestanding Few-layer ReS2

Abstract

Rhenium disulfide (ReS2) is a low-symmetry transition metal dichalcogenide (TMDC) 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 stackingdependent thermal conductivity and its thickness evolution in the few-layer regime remain largely unexplored. Here, we have extracted the thermal conductivity of freestanding, few-layer ReS2 samples (thickness < 10 nm) using polarization-resolved optothermal Raman thermometry after correcting for polarization dependent absorbance. All measured 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 non-monotonic dependence on thickness over the 2.5 to 8 nm range which is supported by density functional theory (DFT) 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.