Raman scattering excitation (RSE) is an experimental technique in which the spectrum is made up by sweeping the excitation energy when the detection energy is fixed. We study the low-temperature (T = 5 K) RSE spectra measured on four high quality monolayers (ML) of semiconducting transition metal dichalcogenides (S-TMDs), i.e. MoS₂, MoSe₂, WS₂, and WSe₂, encapsulated in hexagonal BN. The outgoing resonant conditions of Raman scattering reveal an extraordinary intensity enhancement of the phonon modes, which results in extremely rich RSE spectra. The obtained spectra are composed not only of Raman-active peaks, i.e. in-plane E\({}^{{\prime} }\) and out-of-plane A\({}_{1}^{{\prime} }\), but the appearance of 1st, 2nd, and higher-order phonon modes is recognized. The intensity profiles of the A\({}_{1}^{{\prime} }\) modes in the investigated MLs resemble the emissions due to neutral excitons measured in the corresponding PL spectra for the outgoing type of resonant Raman scattering conditions. Furthermore, for the WSe₂ ML, the A\({}_{1}^{{\prime} }\) mode was observed when the incoming light was in resonance with the neutral exciton line. The strength of the exciton-phonon coupling (EPC) in S-TMD MLs strongly depends on the type of their ground excitonic state, i.e. bright or dark, resulting in different shapes of the RSE spectra. Our results demonstrate that RSE spectroscopy is a powerful technique for studying EPC in S-TMD MLs.

拉曼散射激发（RSE）是一种在检测能量固定的情况下，通过扫描激发能量来构成光谱的实验技术。我们研究了封装 在半导体过渡金属二硫化物 (S-TMD) 的四个高质量单层 (ML)（即 MoS ₂、MoSe ₂、WS ₂和 WSe ₂ ）上测量的低温 ( T = 5 K) RSE 光谱。六方BN。拉曼散射的传出共振条件揭示了声子模式的非凡强度增强，从而产生极其丰富的 RSE 光谱。获得的光谱不仅由拉曼活性峰组成，即面内 E \({}^{{\prime} }\)和面外 A \({}_{1}^{{\ prime} }\)，但可以识别一阶、二阶和高阶声子模式的出现。所研究的 ML 中A \({}_{1}^{{\prime} }\)模式的强度分布类似于在相应 PL 光谱中测量的中性激子发射，用于出射类型的共振拉曼散射条件。此外，对于WSe ₂ ML，当入射光与中性激子线共振时，观察到A \({}_{1}^{{\prime} }\)模式。S-TMD ML 中激子-声子耦合 (EPC) 的强度很大程度上取决于其基激子态的类型，即亮或暗，从而导致 RSE 光谱的不同形状。我们的结果表明，RSE 光谱是研究 S-TMD ML 中 EPC 的强大技术。