Electron–phonon interaction in bulk and nanoflakes of MoS2 is investigated using Raman spectroscopy. Resonant Raman spectroscopic studies carried out on bulk and liquid exfoliated nanoflakes of MoS2 revealed a second order Raman mode (called the “b” mode), whose frequency in the case of nanoflakes was found to be largely different from that in bulk MoS2. Temperature dependent Raman spectra show larger variation in the frequency of the “b” mode in bulk MoS2 as compared to that in nanoflakes of MoS2. This anomalous behavior of the “b” mode could be attributed to the stronger electron–phonon coupling occurring in bulk MoS2, due to higher electron concentration in the same, as compared to that in nanoflakes of MoS2. A larger sulfur vacancy in bulk MoS2 as compared to that of nanoflakes was found to be responsible for higher electron concentrations. These findings are supported by energy dispersive x-ray analysis and x-ray photoelectron spectroscopic studies carried out on bulk and nanoflakes of MoS2. The present study suggests a more sensitive probe for the estimation of electron concentrations in the low limit range by following the “b” mode in resonance Raman spectra.

中文翻译：

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使用共振拉曼光谱中的异常“b”模式研究 MoS2 块状和纳米薄片中的电子 - 声子相互作用

使用拉曼光谱研究了 MoS2 块状和纳米薄片中的电子-声子相互作用。对 MoS2 的块状和液体剥离纳米薄片进行的共振拉曼光谱研究揭示了二阶拉曼模式（称为“b”模式），发现纳米薄片的频率与块状 MoS2 的频率有很大不同。与温度相关的拉曼光谱显示，与 MoS2 纳米薄片相比，块状 MoS2 中“b”模式的频率变化更大。“b”模式的这种异常行为可能是由于与 MoS2 纳米薄片相比，MoS2 中的电子浓度更高，因此在块状 MoS2 中发生了更强的电子 - 声子耦合。与纳米薄片相比，MoS2 中更大的硫空位被发现是导致更高电子浓度的原因。这些发现得到了对 MoS2 的块状和纳米薄片进行的能量色散 X 射线分析和 X 射线光电子能谱研究的支持。本研究提出了一种更灵敏的探针，通过遵循共振拉曼光谱中的“b”模式来估计下限范围内的电子浓度。