Abstract
Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1. The phonon modes are assigned by comparing the peak positions with theoretical calculations. The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. The A1g mode is enhanced at 1.58 and 3.82 eV, which are near the A exciton energy and the band-to-band transition between higher energy bands, respectively. The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy. The different enhancements of the A1g and E2g1 modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies.
Highlights
Raman investigation of MoSe2 was carried out with eight different excitation energies
Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1
The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy
Summary
The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies. The thickness and fine structure of such a layer affect the performance of the solar cell significantly[6,7,8] Both MoS2 and MoSe2 have indirect band gaps for the bulk materials and become direct for monolayer. Raman spectroscopy is a powerful tool to study the structural properties of graphene and 2-dimensional materials and is commonly used to determine the number of layers[14,15,16]. Resonance effects can be used to shed light on the electronic structure
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