Reduction in thermal conductivity of monolayer WS₂ caused by substrate effect

Understanding the substrate and temperature effect on thermal transport properties of transition metal dichalcogenides (TMDs) monolayers are crucial for their future applications. Herein, a dual-wavelength flash Raman (DF-Raman) method is used to measure the thermal conductivity of monolayer WS₂ at a temperature range of 200–400 K. High measurement accuracy can be guaranteed in this method since the influence of both the laser absorption coefficient and temperature-Raman coefficient can be eliminated through normalization. The room-temperature thermal conductivity of suspended and supported WS₂ are 28.5 ± 2.1 (30.3 ± 2.0) and 15.4 ± 1.9 (16.9 ± 2.1) W/(m·K), respectively, with a ~ 50% reduction due to substrate effect. Molecular dynamics (MD) simulations reveal that the suppression of acoustic phonons is mainly responsible for the striking reduction. The behaviors of optical phonons are also unambiguously investigated using Raman spectroscopy, and the in-plane optical mode, E ${}_{2\mathrm{g}}^1$(Γ), is surprisingly found to be slightly enhanced while out-of-plane mode, A_1g(Γ), is suppressed due to substrate interaction, mutually verified with MD results. Our study provides a solid understanding of the phonon transport behavior of WS₂ with substrate interaction, which provides guidance for TMDs-based nanodevices.