Layer number and stacking order-dependent thermal transport in molybdenum disulfide with sulfur vacancies

Recent theoretical works on two-dimensional molybdenum disulfide, MoS$_2$, with sulfur vacancies predict that the suppression of thermal transport in MoS$_2$ by point defects is more prominent in monolayers and becomes negligible as layer number increases. Here, we investigate experimentally the thermal transport properties of two-dimensional molybdenum disulfide crystals with inherent sulfur vacancies. We study the first-order temperature coefficients of interlayer and intralayer Raman modes of MoS$_2$ crystals with different layer numbers and stacking orders. The in-plane thermal conductivity ($\kappa$) and total interface conductance per unit area ($g$) across the 2D material-substrate interface of mono-, bi- and tri-layer MoS$_2$ samples are measured using the micro-Raman thermometry. Our results clearly demonstrate that the thermal conductivity is significantly suppressed by sulfur vacancies in monolayer MoS$_2$. However, this reduction in $\kappa$ becomes less evident as the layer number increases, confirming the theoretical predictions. No significant variation is observed in the $\kappa$ and $g$ values of 2H and 3R stacked bilayer MoS$_2$ samples

High temperature anomalous Raman and photoluminescence response of molybdenum disulfide with sulfur vacancies

Abstract We report an intriguing anomalous behavior observed in the temperature-dependent Raman spectra of mono-, bi-, and trilayer molybdenum disulfide samples with sulfur vacancies, measured at high temperatures ranging from room temperature to 463 K. In contrast to existing reports, we observed a decrease in the FWHM of the A $$_{1g}$$ 1 g phonon mode, along with an increase in the relative intensity of the A $$_{1g}$$ 1 g mode to the E $$_{2g}^1$$ 2 g 1 mode, as the temperature increased. This trend becomes less prominent as the layer number increases from monolayer, disappearing entirely in few-layer samples. Additionally, we observed an intensity enhancement in the photoluminescence spectra of MoS2 samples at high temperatures (up to 550 K), which depends on the layer number. These observations are explained by considering the presence of sulfur vacancies, their interaction with the environment, electron density reduction, and a phonon-mediated intervalley charge transfer at elevated temperatures. Our results unambiguously establish that the effect of defects (sulfur vacancies) is more prominently reflected in the temperature dependence of FWHM and the relative intensity of the Raman modes rather than in the Raman peak positions