Resonant Raman scattering in the infrared: the case of MoSe 2

We investigate Raman scattering of MoSe 2 crystals with excitation energies in the visible and in the infrared (from 1.16 eV to 2.33 eV). We show that, despite the lower scattering efficiency at longer wavelengths, it is possible to measure also MoSe 2 monolayers with photon energy of 1.16 eV, by placing the flakes on hexagonal BN slabs on Au substrates.The lineshape of the Raman modes is shown to be highly dependent on the excitation energy due to resonant processes. In particular, we observe effects of resonant Raman scattering with the indirect band gap (1.14 eV) of MoSe 2 yielding information on the electronic and phonon density of states. By the calculation of the two-phonon density of states in different position of the Brillouin zone, we are able to reproduce some experimental features of the second order Raman spectra.