Raman scattering in few-layer MoTe$_{2}$

TL;DR

This study investigates the Raman scattering properties of few-layer MoTe$_{2}$ crystals at room temperature, revealing complex vibrational mode structures and their dependence on excitation wavelength, with implications for understanding interlayer interactions.

Contribution

The paper provides a detailed analysis of vibrational modes in few-layer MoTe$_{2}$, including a linear chain model for interlayer vibrations and the effect of excitation wavelength on spectral complexity.

Findings

Out-of-plane vibrational modes show complex structures explained by interlayer interactions.

Low-energy shear and breathing modes' energies are well modeled by a linear chain with nearest neighbor interactions.

Raman spectra differ significantly between 632.8 nm and 514.5 nm excitation wavelengths, indicating resonance effects.

Abstract

We report on room-temperature Raman scattering measurements in few-layer crystals of exfoliated molybdenum ditelluride (MoTe$_{2}$) performed with the use of 632.8 nm (1.96 eV) laser light excitation. In agreement with recent study reported by G. Froehlicher et al, (2015 $Nano$ $Lett.$ 15 6481) we observe a complex structure of the out-of-plane vibrational modes (A$_{1g}$/A$^{'}_{1}$), which can be explained in terms of interlayer interactions between single atomic planes of MoTe$_{2}$. In the case of low-energy shear and breathing modes of rigid interlayer vibrations it is shown that their energy evolution with the number of layers can be well reproduced within a linear chain model with only the nearest neighbor interaction taken into account. Based on this model the corresponding in-plane and out-of-plane force constants are determined. We also show that the Raman scattering in MoTe$_{2}$ measured using 514.5 nm (2.41 eV) laser light excitation results in much simpler spectra. We argue that the rich structure of the out-of-plane vibrational modes observed in Raman scattering spectra excited with the use of 632.8 nm laser light results from its resonance with the electronic transition at the M or K points of the MoTe$_{2}$ first Brillouin zone.