Substrate effect on thermal conductivity of monolayer WS2: Experimental measurement and theoretical analysis

TL;DR

This study measures and analyzes how substrates affect the thermal conductivity of monolayer WS2, revealing a significant reduction due to substrate-induced phonon scattering, with implications for device thermal management.

Contribution

It provides the first combined experimental and theoretical analysis of substrate effects on WS2's thermal conductivity, including molecular dynamics simulations and Raman spectroscopy insights.

Findings

Supported WS2 has ~50% lower thermal conductivity than suspended WS2.

Substrate increases phonon scattering and doping levels, reducing phonon lifetime.

The study offers comparative data for other TMDCs and guides device design.

Abstract

Monolayer WS2 has been a competitive candidate in electrical and optoelectronic devices due to its superior optoelectronic properties. To tackle the challenge of thermal management caused by the decreased size and concentrated heat in modern ICs, it is of great significance to accurately characterize the thermal conductivity of the monolayer WS2, especially with substrate supported. In this work, the dual-wavelength flash Raman method is used to experimentally measure the thermal conductivity of the suspended and the Si/SiO2 substrate supported monolayer WS2 at a temperature range of 200 K - 400 K. The room-temperature thermal conductivity of suspended and supported WS2 are 28.45 W/mK and 15.39 W/mK, respectively, with a ~50% reduction due to substrate effect. To systematically study the underlying mechanism behind the striking reduction, we employed the Raman spatial mapping analysis combined with the molecular dynamics simulation. The analysis of Raman spectra showed the increase of doping level, reduction of phonon lifetime and suppression of out-of-plane vibration mode due to substrate effect. In addition, the phonon transmission coefficient was mutually verified with Raman spectra analysis and further revealed that the substrate effect significantly enhances the phonon scattering at the interface and mainly suppresses the acoustic phonon, thus leading to the reduction of thermal conductivity. The thermal conductivity of other suspended and supported monolayer TMDCs (e.g. MoS2, MoSe2 and WSe2) were also listed for comparison. Our researches can be extended to understand the substrate effect of other 2D TMDCs and provide guidance for future TMDCs-based electrical and optoelectronic devices.