Energy Transport State Resolved Raman for Probing Interface Energy Transport and Hot Carrier Diffusion in Few-Layered MoS₂

Quantitative understanding of 2D atomic layer interface thermal resistance (<i>R</i>) based on Raman characterization is significantly hindered by unknown sample-to-sample optical properties variation, interface-induced optical interference, off-normal laser irradiation, and large thermal-Raman calibration uncertainties. In this work, we develop a novel energy transport state resolved Raman (ET-Raman) to resolve these critical issues, and also consider the hot carrier diffusion, which is crucial but has been rarely considered during interface energy transport study. In ET-Raman, by constructing two steady heat conduction states with different laser spot sizes, we differentiate the effect of <i>R</i> and hot carrier diffusion coefficient (<i>D</i>). By constructing an extreme state of zero/negligible heat conduction using a picosecond laser, we differentiate the effect of <i>R</i> and material’s specific heat. In the end, we precisely determine <i>R</i> and <i>D</i> without need of laser absorption and temperature rise of the 2D atomic layer. Seven MoS₂ samples (6.6–17.4 nm) on c-Si are characterized using ET-Raman. Their <i>D</i> is measured in the order of 1.0 cm²/s, increasing against the MoS₂ thickness. This is attributed to the weaker in-plane electron–phonon interaction in thicker samples, enhanced screening of long-range disorder, and improved charge impurities mitigation. <i>R</i> is determined as 1.22–1.87 × 10^–7 K·m²/W, decreasing with the MoS₂ thickness. This is explained by the interface spacing variation due to thermal expansion mismatch between MoS₂ and Si, and increased stiffness of thicker MoS₂. The local interface spacing is uncovered by comparing the theoretical Raman intensity and experimental data, and is correlated with the observed <i>R</i> variation