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Atypical Defect-Mediated Photoluminescence and Resonance Raman Spectroscopy of Monolayer WS₂

Li, Jiake, Su, Weitao, Chen, Fei, Fu, Li, Ding, Su, Song, Kaixin, Huang, Xiwei, Zhang, Lijie
Journal of physical chemistry 2019 v.123 no.6 pp. 3900-3907
Raman spectroscopy, energy, optical properties, photoluminescence, physical chemistry, temperature
Defects play an indispensable role in tuning the optical properties of two-dimensional materials. Herein, we study the influence of defects on the photoluminescence and resonance Raman spectra of as-grown monolayer (1L) WS₂. Increasing the density of defects significantly lowers the excitonic binding energy by up to 110 meV. These defect-modified excitonic binding energies in 1L-WS₂ strongly mediate the Raman resonance condition, resulting in unexpected Raman intensity variations in the LA(M), 2LA(M), and A₁′(Γ) phonon modes. The sample with the highest density of defects exhibits an almost temperature-independent resonance in different Raman modes at low temperature, whereas the samples with low densities of defects exhibit a clear resonance with decreasing temperature. This study will further increase our understanding of the role of defects in resonance Raman spectroscopy and of the phonon–exciton interaction in 1L-WS₂.