Raman scattering from the bulk inactive out–of–plane $${{\bf{B}}}_{{\bf{2}}{\bf{g}}}^{{\bf{1}}}$$ mode in few–layer MoTe2

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 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/ 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.

Emission Excitation Spectroscopy in WS2 Monolayer Encapsulated in Hexagonal BN

“…One of key observations reported in S-TMDs is a strong enhancement of the Raman scattering signal, when excitation energy is in resonance with excitonic complexes [7][8][9]. We have recently shown this effect in monolayer WS 2 on Si/SiO 2 substrate introducing the Raman scattering excitation (RSE) technique [10].…”

Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS$_{2}$

“…in thin layers of 2H-MoTe 2 . 56 Therefore, in the following we will refer to the observed Raman modes using the bulk-related representations, as is usually done in the literature.…”

Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

“…the intensity maxima as a function of temperature, has not been reported so far for other layered materials. Particularly, for thin layers of S-TMDs, only a growth or a decrease of the RS signal was observed in a broad temperature range from 5 K to 300 K [22][23][24] . The most interesting result is the strong vanishing of all modes intensities at temperatures above around 280 K under excitations of 1.96 eV and 2.41 eV in GaSe and InSe, respectively.…”

“…This offers supplementary information on the coupling of particular phonons to electronic transitions of a specific symmetry [19][20][21] . The crossover between the non-resonant and resonant conditions can be achieved not only by the variation of the excitation energy but also by the modulation of temperature as it was recently reported [22][23][24] . In such an approach, it is the band structure that changes with temperature allowing for resonance with particular excitation energy.…”