The effect of bis(trifluoromethane) sulfonimide (TFSI, superacid) treatment on the optical properties of MoS₂ monolayers is investigated by means of photoluminescence, reflectance contrast and Raman scattering spectroscopy employed in a broad temperature range. It is shown that when applied multiple times, the treatment results in progressive quenching of the trion emission/absorption and in the redshift of the neutral exciton emission/absorption associated with both the A and B excitonic resonances. Based on this evolution, a trion complex related to the B exciton in monolayer MoS₂ is unambiguously identified. A defect-related emission observed at low temperatures also disappears from the spectrum as a result of the treatment. Our observations are attributed to effective passivation of defects on the MoS₂ monolayer surface. The passivation reduces the carrier density, which in turn affects the out-of-plane electric field in the sample. The observed tuning of the carrier concentration strongly influences also the Raman scattering in the MoS₂ monolayer. An enhancement of Raman scattering at resonant excitation in the vicinity of the A neutral exciton is clearly seen for both the out-of-plane A′₁ and in-plane E′ modes. On the contrary, when the excitation is in resonance with a corresponding trion, the Raman scattering features become hardly visible. These results confirm the role of the excitonic charge state plays in the resonance effect of the excitation energy on the Raman scattering in transition metal dichalcogenides.

通过在宽温度范围内使用的光致发光，反射率对比和拉曼散射光谱研究了双（三氟甲烷）磺酰亚胺（TFSI，超强酸）处理对MoS ₂单层光学性能的影响。已表明，当多次使用时，该处理导​​致三重子发射/吸收的逐步淬灭以及与A和B激子共振相关的中性激子发射/吸收的红移。基于这种演化，与单分子MoS _2中的B激子有关的三元络合物被明确识别。处理后，在低温下观察到的与缺陷相关的发射也从光谱中消失了。我们的观察结果归因于MoS ₂单层表面上缺陷的有效钝化。钝化会降低载流子密度，进而影响样品中的平面外电场。观察到的载流子浓度的调整也强烈影响了MoS ₂单层中的拉曼散射。拉曼的在A中性激子的附近，共振激发散射的增强是清楚地看到两者的外的平面A' ₁和平面E'模式。相反，当激发与相应的三极子共振时，几乎看不见拉曼散射特征。这些结果证实了激子电荷态在激发能对过渡金属二卤化物中拉曼散射的共振效应中的作用。