Abstract
We report a study of Raman scattering in few-layer MoTe2 focused on high-frequency out-of-plane vibrational modes near 291 cm−1 which are associated with the bulk-inactive {{rm{B}}}_{2{rm{g}}}^{1} mode. Our temperature-dependent measurements reveal a double peak structure of the feature related to these modes in the Raman scattering spectra of 4- and 5-layer MoTe2. In accordance with literature data, the doublet’s lower- and higher-energy components are ascribed to the Raman-active A1g/{{bf{A}}{boldsymbol{^{prime} }}}_{{bf{1}}} vibrations involving, respectively, only the inner and surface layers. We demonstrate a strong enhancement of the inner mode’s intensity at low temperature for 1.91 eV and 1.96 eV laser light excitation which suggests a resonant character of the Raman scattering processes probed under such conditions. A resonance of the laser light with a singularity of the electronic density of states at the M point of the MoTe2 Brillouin zone is proposed to be responsible for the observed effects.
Highlights
We report a study of Raman scattering in few-layer MoTe2 focused on high-frequency out-of-plane vibrational modes near 291 cm−1 which are associated with the bulk-inactiveB21g mode
We propose that the resonance of the laser light with a singularity of the electronic density of states at the M point of the Brilloiun zone in MoTe2 might be responsible for the observed anomalous increase of the Raman scattering (RS) features
We have investigated Raman scattering from the out-of-plane vibrational modes (A1g/A′1) in few-layer MoTe2 of thickness ranging from one to five layers
Summary
We report a study of Raman scattering in few-layer MoTe2 focused on high-frequency out-of-plane vibrational modes near 291 cm−1 which are associated with the bulk-inactiveB21g mode. The impact of sample’s thickness on the lattice vibrations becomes even stronger when resonant excitation of RS is employed Under such conditions, the resulting change in the electronic configuration of investigated TMD material leads to several effects which cannot be studied with non-resonant RS measurements, such as the enhancement of particular features in the RS spectrum[17] related to multiphonon processes[18] or quenching of Raman-active modes due to quantum interference[19,20]. Extensively studied low- and mid-frequency oscillations of few-layer TMD crystals, these modes have not received so far much attention Strong enhancement of this phonon peak was first reported by Yamamoto et al.[31], where the appearnce in the RS spectrum was atributed to translation symmetry breaking in thin MoTe2 layers. We propose that the resonance of the laser light with a singularity of the electronic density of states at the M point of the Brilloiun zone in MoTe2 might be responsible for the observed anomalous increase of the RS features
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