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

Abstract

We first report the temperature phonon properties of a large-area thin film (lateral size: ∼mm, thickness ∼50 nm) made from WS 2 mono and few layers deposited on the SiO 2 /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 (κ = 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 (κ and g) are 1 order of magnitude lower than that for bulk or monolayer WS 2 , 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.

Measurement of Thermal Conductivity of Suspended and Supported Single-Layer WS2 Using Micro-photoluminescence Spectroscopy

“…Compared with the Raman spectra measured with ∼150 grooves/mm grating, much higher resolution E 2g 1 peak (∼352 cm −1 ) and A 1g peak (∼418 cm −1 ) are observed. 32 The Raman intensity mapping of the entire film (see the inset) reflects the uniformity of the WS 2 film. Once the Raman signals are acquired with the grating of ∼2400 grooves/mm rather than ∼150 grooves/mm, compared to the PL signal measured with the ∼150 grooves/mm grating, the intensities of the Raman signal are reduced by a factor of ∼100.…”

“…However, the accuracy of the Raman thermometry method mainly depends on the resolution of the micro-Raman spectrometer, which necessitates gratings of ∼2400 grooves/mm with high density, and the corresponding Raman signal is plotted as a red curve in Figure c. Compared with the Raman spectra measured with ∼150 grooves/mm grating, much higher resolution E 2 g 1 peak (∼352 cm –1 ) and A 1g peak (∼418 cm –1 ) are observed . The Raman intensity mapping of the entire film (see the inset) reflects the uniformity of the WS 2 film.…”

Visualization of Strain-Engineered Nanopattern in Center-Confined Mesoscopic WS2 Monolayer Flakes

“…The equilateral hexagon nucleation of length 7 μm was fixed in the center. The elastic moduli of the WS 2 and SiO 2 were set as 240 and 70 GPa, and the thermal expansion coefficients of the WS 2 and SiO 2 are 6 × 10 –6 and 2 × 10 –7 /K, respectively. ,− The initial and final temperatures were set to 1298 and 298 K, respectively, to simulate the thermal mismatch stress/strain behavior between the WS 2 flake and SiO 2 substrate during the cooling process.…”

Low Energy Switching of Phase Change Materials Using a 2D Thermal Boundary Layer

“…We used the κ values of a-GeTe (∼0.204 W·m –1 ·K –1 ) and c-GeTe (∼3.59 W·m –1 ·K –1 ) . Thermal boundary conductances of MoS 2 and WS 2 layers were used as ∼16 and ∼5.5 MW·m –2 ·K –1 . , The thickness of the GeTe was ∼30 nm, and w was measured as 0.8 μm. Laser pulses (100 and 500 ns) with different powers were applied in amorphization and crystallization simulations respectively.…”