Temperature dependent Raman spectroscopy of shear and layer breathing modes in bilayer MoS₂

We report low-frequency Raman scattering results of bilayer (2L) MoS₂ structures with 3R and 2H stacking orders. The stacking orders were identified by Raman mapping images of the low-frequency shear (S) and layer breathing (B) modes. Linear temperature coefficients (χ) were obtained from temperature-dependent frequency changes of the shear and layer breathing modes for the 3R- and 2H-stacked 2L MoS₂: χ_3R^S=−0.011±0.006cm⁻¹/K, χ_2H^S=−0.009±0.002cm⁻¹/K, χ_3R^B=−0.009±0.003cm⁻¹/K, and χ_2H^B=−0.010±0.002cm⁻¹/K. Interestingly, the temperature coefficients were significantly reduced after the MoS₂ samples were thermally heated: χ_3R^S=−0.004±0.001cm⁻¹/K, χ_2H^S=−0.004±0.001cm⁻¹/K, χ_3R^B=−0.002±0.001cm⁻¹/K, and χ_2H^B=−0.002±0.001cm⁻¹/K. Similar behaviors were also observed for the temperature coefficients of the high-frequency E_2g¹ and A_1g phonons. The heating-induced modifications in the temperature coefficients are attributed to changes in the MoS₂–substrate coupling. Our result further paves the way for optimal design strategies for low-dimensional device applications where thermal management plays a crucial role in device performance.