Rigid-layer Raman-active modes in $N$-layer Transition Metal Dichalcogenides: interlayer force constants and hyperspectral Raman imaging

TL;DR

This study investigates the rigid-layer Raman-active modes in various N-layer transition metal dichalcogenides, extracting interlayer force constants and demonstrating high-precision hyperspectral Raman imaging of layered domains.

Contribution

It provides a comparative analysis of interlayer modes across different phases and introduces a linear chain model to determine interlayer force constants.

Findings

Rigid layer modes appear as well-defined features in 0-40 cm$^{-1}$ range.

Interlayer force constants are of similar magnitude across different materials.

Hyperspectral Raman imaging can precisely map N-layer domains.

Abstract

We report a comparative study of rigid layer Raman-active modes in $N$-layer transition metal dichalcogenides. Trigonal prismatic (2Hc, such as MoSe$_2$, MoTe$_2$, WS$_2$, WSe$_2$) and distorted octahedral (1T', such as ReS$_2$ and ReSe$_2$) phases are considered. The Raman-active in-plane interlayer shear modes and out-of-plane interlayer breathing modes appear as well-defined features with wavenumbers in the range 0-40~cm$^{-1}$. These rigid layer modes are well-described by an elementary linear chain model from which the interlayer force constants are readily extracted. Remarkably, these force constants are all found to be of the same order of magnitude. Finally, we show that the prominent interlayer shear and breathing mode features allow high-precision hyperspectral Raman imaging of $N-$layer domains within a given transition metal dichalcogenide flake.