  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.
