Two-Dimensional Transition-Metal Dichalcogenides by Alexander V. Kolobov & Junji Tominaga

Author:Alexander V. Kolobov & Junji Tominaga
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

7.9.1.2 Wavelength Dependence

Resonance Raman scattering in single-layer measured using different excitation wavelengths [79] is shown in Fig. 7.36. Like in the bulk, despite the gap opening and a transition to a direct gap , the resonance still occurs at 633 nm (1.96 eV) and 594 nm (2.09 eV). It was proposed that the resonance is always dominated by the excitonic excitations at in both bulk and single-layer . One difference between the resonance spectra of the bulk and single-layer is the gradual lift-up of background towards high frequencies in monolayer , which was attributed to the tail of the extremely strong photoluminescence in monolayer . A significant difference between bulk and monolayer in resonance Raman spectra is that almost all the first-order and multi-phonon modes were greatly broadened and their relative intensities were substantially changed in monolayer . The sharp multi-phonon modes above 550 cm in the resonance spectra of the bulk were strongly suppressed and almost invisible in the monolayer case, in agreement with the results of [80].

Fig. 7.36Room-temperature Raman spectra of monolayer under different excitation wavelengths. The inset shows the frequency separation between the and modes, which demonstrates that the sample is monolayer [79]. Reprinted with permission. Copyright 2014 by the American Institute of Physics

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