Effects of hot phonons and thermal stress in micro-Raman spectra of molybdenum disulfide
Effects of hot phonons and thermal stress in micro-Raman spectra of molybdenum disulfide
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DOI：
10.1063/5.0122945
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发表时间：
2022-06
影响因子：
4
通讯作者：
Peter Sokalski;Zherui Han;G. Fleming;Brandon Smith;Sean E. Sullivan;R. Huang;X. Ruan;Li Shi
中科院分区：
文献类型：
--
作者：
Peter Sokalski;Zherui Han;G. Fleming;Brandon Smith;Sean E. Sullivan;R. Huang;X. Ruan;Li Shi
显微拉曼光谱已成为探测功能材料热物理性质的重要工具。通过聚焦的拉曼激发激光束的局部加热可以在材料中产生应力和局部非平衡声子。在这里，我们调查的热光学声子的影响，在拉曼光谱的二硫化钼，并区分它们从热致压缩应力，这会导致一个拉曼频率蓝移所造成的。我们使用热机械分析来校正从测量的拉曼峰位移中提取的等效晶格温度中的这种应力效应。当加热高斯激光束减小到0.71 μm时，修正后的峰移温升分别比未经应力修正时由实测峰移和线宽确定的值高17%和8%，比由反斯托克斯与斯托克斯强度比确定的光学声子温升小32%。当束宽增加到1.53 μm时，热光学声子与晶格之间的这种非平衡消失。比先前悬浮石墨烯的显微拉曼测量中报道的那些不太明显，这种观察到的热声子行为与基于第一原理的多温度模型相一致，该模型与布里渊区中的其他光学声子和这种原型过渡金属二硫属化物的声学声子相比，过于密集的区中心光学声子。这些发现提供了对这种新兴电子和光电材料中能量弛豫过程的详细了解，并澄清了这种和其他二维材料中热输运的显微拉曼测量中的一个重要问题。
Micro-Raman spectroscopy has become an important tool in probing thermophysical properties in functional materials. Localized heating by the focused Raman excitation laser beam can produce both stress and local nonequilibrium phonons in the material. Here, we investigate the effects of hot optical phonons in the Raman spectra of molybdenum disulfide and distinguish them from those caused by thermally induced compressive stress, which causes a Raman frequency blue shift. We use a thermomechanical analysis to correct for this stress effect in the equivalent lattice temperature extracted from the measured Raman peak shift. When the heating Gaussian laser beam is reduced to 0.71 μm, the corrected peak shift temperature rise is 17% and 8%, respectively, higher than those determined from the measured peak shift and linewidth without the stress correction, and 32% smaller than the optical phonon temperature rise obtained from the anti-Stokes to Stokes intensity ratio. This nonequilibrium between the hot optical phonons and the lattice vanishes as the beam width increases to 1.53 μm. Much less pronounced than those reported in prior micro-Raman measurements of suspended graphene, this observed hot phonon behavior agrees with a first-principles based multitemperature model of overpopulated zone-center optical phonons compared to other optical phonons in the Brillouin zone and acoustic phonons of this prototypical transition metal dichalcogenide. The findings provide detailed insight into the energy relaxation processes in this emerging electronic and optoelectronic material and clarify an important question in micro-Raman measurements of thermal transport in this and other two-dimensional materials.