Excitation energy dependent Raman spectrum of MoSe2

Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E-1g, A(1g1), E-2g(1), and A(2u)(2) peaks are observed in the range of 100-400cm(-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 A(1g) 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 E-2g(1) mode is strongly enhanced with respect to the A(1g) mode for the 2.71- and 2.81-eV excitations, which are close to the Cexciton energy. The different enhancements of the A(1g) and E-2g(1) modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including Els and A(2u)(2) are forbidden but appear due to the resonance effect near optical transition energies.