Phonon and Thermal Properties of Thin Films Made from WS2 Mono- and Few-Layer Flakes

We first report the temperature phonon properties of a large-area thin film (lateral size: similar to mm, thickness similar to 50 nm) made from WS2 mono and few layers deposited on the SiO2/Si substrate. We show that temperature phonon properties probed by Raman spectroscopy significantly differ for bulk and thin-film systems in a temperature range of 90-450 K; however, both exhibit strong temperature-dependent phonon energy nonlinear behavior. Employing the optothermal Raman method, we also estimate thin-film thermal conductivity (kappa = 4.3 W/(m K)) and thermal interface conductance (g = 5.5 MW/(m(2) K)) at room temperature. We find that the thermal properties of thin films (kappa and g) are 1 order of magnitude lower than that for bulk or monolayer WS2, which is caused by a reduction in flake size and an increase in boundary scattering. This finding is important for heat management in future applications of thin films made from two-dimensional (2D) nanoflakes.